What Investing Mistakes Should I Avoid? The Ones Wall Street Is Counting On You to Keep Making

The Question You Should Have Been Asking All Along

If you are searching for the investing mistakes you should avoid, I want to start by telling you something that the financial services industry spends enormous amounts of money making sure you never hear: most of the mistakes that cost ordinary investors the most are not mistakes you are making. They are mistakes that the system has been designed to encourage you to make, because those mistakes are the engine of the industry's profitability. The confusion is not accidental. The complexity is not incidental. The opacity around fees, incentives, and the actual performance of the products being sold to you is structural, deliberate, and sustained by an entire ecosystem of people who benefit from your continued ignorance.

I say this not as an outsider looking in but as someone who spent years inside that ecosystem. I held senior positions at Cantor Fitzgerald, DE Shaw, and the LeFrak Organization. I managed limited partnerships and discretionary funds for large hedge funds, banks, and family offices. I know how the machine works from the inside, and I know how wide the gap is between how it presents itself to clients and how it actually operates. That gap is the subject of everything I want to say here. Because the most expensive mistakes you are making with your money are not about which stocks you picked or which funds you chose — they are about the fundamental assumptions you are operating under about whose interests are actually being served when you sit across from a financial advisor.

The investing mistakes that matter most are not the dramatic ones — the meme stocks, the panicked sells, the FOMO-driven buys that everyone talks about. Those are real, and I will get to them. But the mistakes that quietly compound over decades and steal the most from your retirement, your financial independence, and your ability to ever actually use the wealth you built — those are structural. They are baked into the relationship you have with your money manager, the products inside your portfolio, and the narrative about investing complexity that the industry maintains because it benefits from your belief that you cannot possibly navigate this without their help. You can. But first you have to understand what you are actually navigating.

The Most Expensive Mistake: Paying for Underperformance

Let me start with the one that costs investors the most money and generates the least outrage, because it is the most effectively hidden. The financial services industry has built an entire business model around the premise that active management — having professional money managers select investments on your behalf — produces superior returns that justify the substantial fees charged. The evidence for this premise is, at best, deeply ambiguous. At worst, it is a myth maintained for the financial benefit of the industry and to the consistent detriment of the investors it serves.

The data on active management performance versus passive index funds has been studied extensively and consistently over decades. The conclusion that emerges, again and again, across different time periods, different asset classes, and different market conditions, is that the overwhelming majority of actively managed funds underperform their benchmark index over any period of ten years or more, net of fees. This is not a controversial finding among researchers. It is among the most replicated results in financial economics. And yet the active management industry continues to capture the majority of professionally managed assets, continues to charge fees that are multiples of what passive alternatives cost, and continues to present its services as the sophisticated choice for serious investors. The sophistication, it turns out, belongs primarily to the marketing.

What makes this particularly consequential for long-term investors is the mathematics of fee drag. The difference between paying 1 percent annually in fees versus 0.1 percent sounds negligible in any given year. Over thirty years, compounded, the difference is staggering. A million-dollar portfolio subjected to a 1 percent annual fee differential loses roughly a third of its potential terminal value compared to the lower-cost alternative — not because of bad investment decisions, but purely because of the cost structure. The financial industry understands this math better than almost anyone. Matthew Sadowsky, then director of retirement and annuities at TD Ameritrade, said it plainly: fees can put a drag on investment performance and impact portfolio value over the long term. That is the polite, measured version of what I would put more directly: the fee structure of most actively managed portfolios is one of the most reliable predictors of long-term underperformance, and the industry knows it.

The reason this mistake persists is not investor irrationality. It is investor trust — a trust that has been carefully cultivated through professional relationships, polished presentations, and the entirely understandable human tendency to believe that complexity is evidence of value. When a financial advisor presents a portfolio of proprietary products with sophisticated-sounding names and multi-layered fee structures, it feels like expertise. It is often the opposite. The complexity is frequently not in the service of the investor's return. It is in the service of the advisor's revenue. Understanding that distinction is the single most financially consequential thing an investor can do.

The Conflict of Interest Nobody Explained to You

Here is a piece of structural reality that the financial services industry has fought hard, through lobbying and regulatory capture, to avoid being required to disclose clearly: many of the people who present themselves as your financial advisor are not legally obligated to act in your best interest. The fiduciary standard — the legal requirement to put the client's interest ahead of your own — does not apply to all financial professionals. Brokers and many commission-based advisors are held to a lower standard: they must recommend products that are "suitable" for you. Suitable is not the same as optimal. Suitable means the product is not obviously inappropriate for your situation. It does not mean it is the best choice. It does not mean it is the lowest cost. It does not mean the advisor's compensation structure had no influence on why they recommended it over alternatives.

This distinction has enormous practical consequences. An advisor working under the suitability standard can recommend a mutual fund with a 1 percent expense ratio and a sales load over an identical index fund with a 0.05 percent expense ratio, as long as the more expensive fund is not unsuitable for your portfolio. They can do this while collecting a commission from the fund company that the index fund alternative would not have generated. They can do this repeatedly, across your entire portfolio, year after year, without ever technically violating any legal obligation to you. The investor, who trusted that "my financial advisor" means someone working on their behalf, has no idea that this is what's happening. And the industry has spent extraordinary resources making sure that investor never asks the right questions to find out.

In Demand Transparency, the book that grew out of my years of watching this dynamic operate at close range, I tried to name this clearly: if investors were to switch en masse to index funds and other forms of passive investment, the Wall Street-industrial complex would crumble. That observation, made by a University of Michigan law professor and cited by others in academic research on the financial industry, is not hyperbole. It is a description of the dependency the industry has on investor inertia, investor deference, and investor trust in a relationship whose terms most investors have never actually examined. The most important investing mistake you can make is failing to examine those terms.

Emotional Investing: The Mistake That Feels Like Wisdom

Beyond the structural issues — the fees, the conflicts of interest, the suitability gap — there is a category of investing mistakes that investors bring to the table themselves, independent of the industry's incentive problems. These are the behavioral mistakes, and they are driven not by ignorance but by emotions that are entirely understandable and genuinely difficult to override. The most costly of these is the pattern of buying high and selling low — the mirror image of the rational strategy, executed reliably by millions of people in moments of market stress and market euphoria.

The buying high error is driven by FOMO and narrative. When a particular asset class, sector, or individual security has been performing exceptionally well and the story around it is compelling and widely covered, the pull to participate is powerful. The performance feels like evidence of an underlying quality, and the social reinforcement of watching others profit creates a sense of urgency that overrides the patient investor's first principle: the best time to buy something is not after it has already gone up. Most retail investors' money flows into the hottest investments at or near their peak, because that is when the narrative is loudest and the social proof is most overwhelming. The resulting performance is predictably disappointing, and the disappointment generates its own emotional response: the selling low error.

The selling low error is driven by fear and loss aversion, which is the well-documented human tendency to experience losses approximately twice as painfully as equivalent gains feel pleasurable. When a portfolio drops 20 percent, the emotional urgency to stop the pain — to sell and get to cash and halt the bleeding — can become overwhelming. The rational calculation, which is that a market decline is a reduction in price and not necessarily a reduction in underlying value, is very difficult to hold onto when the account statement is landing in your inbox every day and the financial news is describing the decline in apocalyptic terms. Most investors who sell during market downturns lock in permanent losses that a patient investor who simply held would have recovered from, often within years.

The reason these behavioral patterns are so persistent is that they are not irrational in isolation — they are rational responses to the emotional experience of watching your money move in uncomfortable directions, applied in the wrong context. A person who moves quickly to stop a loss in most areas of life is behaving adaptively. In long-term investing, that same instinct is consistently counterproductive. The most effective antidote is a written investment policy — a document that specifies your asset allocation, your rebalancing triggers, and your commitment to staying invested through volatility — that you commit to before the emotional pressure arrives, so that you are not making portfolio decisions in a state of maximum stress with the cognitive impairment that emotional arousal reliably produces.

The 401(k) Trap: When Complexity Is Used Against You

The retirement savings system in the United States is a particularly vivid example of how complexity can be deployed against the interests of the people it is ostensibly designed to serve. Research published in the Yale Law Journal found that excessive fees and dominated funds — funds that are objectively inferior to alternatives available in the same plan — were a pervasive problem in 401(k) plans. A Business Wire report cited a survey finding that three-quarters of Americans are in the dark when it comes to 401(k) fees. Those two findings together describe a system in which the people least equipped to evaluate the cost structure of their retirement savings are being systematically charged more than necessary, with their confusion about the fees functioning as a feature rather than a bug of the system.

The 401(k) fee structure is deliberately opaque. Expense ratios are embedded in fund performance numbers rather than disclosed as separate line items, which means most participants never see them as a cost at all. Administrative fees, record-keeping fees, and revenue-sharing arrangements between plan administrators and fund companies add additional layers that are disclosed in documents most participants never read. The net effect is that a significant portion of the returns that participants believe they are earning are being captured by the intermediaries in the system, with no meaningful disclosure and no practical way for the typical participant to identify or challenge the arrangement.

The practical response to this is not to abandon the 401(k) — the tax deferral benefits are real and significant, and the employer match, where it exists, is genuinely free money that should always be captured. The practical response is to make the most of whatever low-cost index fund options are available in the plan, to minimize the use of actively managed funds with high expense ratios, and to advocate through the employer for plan options that serve participants rather than intermediaries. Most people never do this because they assume the plan was designed in their interest. Understanding that it was designed by a committee of interests, of which theirs is only one, changes the approach entirely.

The Story You Tell Yourself About Risk

One of the most underappreciated investing mistakes is the mismatch between the risk tolerance an investor believes they have and the risk tolerance they actually demonstrate when markets move against them. This is not a failure of honesty — it is a failure of imagination. In a stable or rising market, most people genuinely believe they can stomach a 30 or 40 percent portfolio decline. They have read about market cycles, they understand the math of long-term compounding, they have a rational framework for thinking about volatility as the price of long-term returns. And then the portfolio drops 30 percent, and the rational framework collides with the visceral reality of watching a substantial portion of their financial security disappear from a screen, and what they discover is that the person they are in a declining market is not the person they imagined they would be in a rising one.

The investing mistake here is constructing a portfolio for the hypothetical, emotionally regulated version of yourself rather than the real, emotionally reactive version. If a portfolio decline of 30 percent would realistically cause you to sell, then a portfolio positioned for a 30 percent decline is not the right portfolio for you — regardless of what the risk tolerance questionnaire said, regardless of what your rational self believes about long-term investing. The cost of being forced out of the market at a low by your own emotional response to loss is higher than the cost of accepting a lower expected return in exchange for a less volatile position. The right portfolio is not the one with the highest expected return. It is the one that you can actually hold through a market cycle without making a destructive behavioral decision at the worst possible moment.

This is one of the places where a genuinely good financial advisor — one operating under a fiduciary standard, compensated by you rather than by product commissions — can provide real value. Not by generating alpha in the portfolio, which the evidence suggests is extremely difficult to do consistently, but by being the voice of reason and process discipline when emotional pressure is highest. The behavior gap — the difference between the return an investment earns and the return an investor captures because of the timing of their entries and exits — is one of the most persistent and documentable sources of wealth destruction in retail investing. A good advisor narrows that gap. A conflicted one, whose compensation depends on recommending active products, widens it.

What Wall Street Is Counting On You Not to Know

The financial services industry's revenue model is, at its core, a bet on your continued inattention. Not your stupidity — your inattention. You are busy. You are running a career, a family, a business, a life. You hired someone to handle the money part because you don't have bandwidth to manage it yourself, and that is a reasonable thing to do. But the hiring of someone to manage it does not mean you are relieved of the responsibility to understand, at a basic level, how that person is compensated, what they are required to do for you by law, and whether the cost structure of your portfolio is working for you or against you.

The questions you should be asking — and that most investors never ask, because the relationship dynamics make them feel rude or presumptuous — are straightforward. How are you compensated? Are you a fiduciary at all times, in writing? What is the total expense ratio of every fund in my portfolio, including any sales loads or 12b-1 fees? What would a comparable portfolio of low-cost index funds look like, and what would it have returned over the last ten years compared to my current portfolio? These are not trick questions or aggressive challenges. They are basic due diligence questions that any competent professional should be able to answer clearly and without defensiveness. If the person managing your money cannot or will not answer them clearly, that itself is information worth acting on.

In Terminal Success by Jason Mandel, I wrote about the way the constant chase for money — and the systems that facilitate it — can consume a person from the inside out. That observation applies to Wall Street's business model as clearly as it applies to the individual investor's psychology. A system optimized for the extraction of fees and the protection of information asymmetry is a system that has been very successfully chasing money, largely at the expense of the people whose money it is managing. Understanding that is not cynicism. It is the minimum level of financial literacy required to protect yourself in a system that is not, by design, protecting you.

The Investing Principles That Actually Hold Up Over Time

After everything I have seen and experienced inside the financial industry, the principles that hold up over time are remarkably simple. They are not exciting. They are not the material for compelling conference presentations or sophisticated-sounding product pitches. But they are the foundations of genuine long-term wealth building, and they work precisely because they resist the complexity that the industry uses to obscure cost and manufacture apparent value.

The first principle worth understanding is that cost is the only variable in investing that is known in advance and entirely within your control. Expected return is probabilistic. Market timing is uncertain. Manager skill is difficult to sustain and nearly impossible to identify in advance. But the fee you are paying every year is certain, it compounds, and it comes directly out of your return. Minimizing cost is not a compromise on quality. For the vast majority of investors, it is the single highest-conviction decision available in portfolio construction.

What compounds this further is the principle of staying invested. The evidence on market timing — the attempt to be in the market when it goes up and out of the market when it goes down — is unambiguous: it does not work reliably, and the transaction costs and tax consequences of frequent repositioning typically ensure that even when the timing calls are right, the net result underperforms a simple buy-and-hold strategy. The enemy of the long-term investor is not the market. It is their own behavior in response to the market's short-term movements. The strategy that addresses this most effectively is the least interesting one available: buy broadly diversified, low-cost index funds, contribute consistently, rebalance periodically, and do not touch it when the news is bad.

And yet here is where it gets uncomfortable: following these principles requires you to accept that you are not going to beat the market, that your financial advisor is probably not going to beat the market, and that the sophisticated-sounding complexity of most investment products is doing more for the person selling them than for the person buying them. That acceptance is, for many high achievers, genuinely difficult. The same drive that produced success in every other domain of life resists the idea that the optimal strategy is one of deliberate ordinariness. But the evidence is unambiguous, and the cost of the alternative — the perpetual pursuit of above-average returns through above-average fees — is one of the most reliably documented wealth destroyers in personal finance.

Frequently Asked Questions

What is the single biggest investing mistake most people make?

The most costly mistake, measured over a lifetime of investing, is paying excessive fees for investment management that does not generate returns to justify those costs. The compounding effect of a 1 percent annual fee differential, sustained over thirty or forty years, removes a substantial fraction of the terminal portfolio value — not through bad investment decisions but through the arithmetic of cost drag. Most investors are unaware of the total cost structure of their portfolios because those costs are embedded in product structures rather than disclosed as explicit line items. Identifying and minimizing those costs is the highest-impact action most investors can take, and it requires neither sophisticated market knowledge nor unusual financial literacy — only the willingness to ask direct questions and demand clear answers.

How does Wall Street make money from individual investors?

The primary mechanism is the sustained capture of a percentage of assets under management, year after year, regardless of whether the management generates value above what a low-cost passive alternative would have delivered. This is supplemented by sales loads and commissions on product transactions, revenue-sharing arrangements between fund companies and plan administrators, and the ongoing maintenance of information asymmetry that makes it difficult for investors to compare the cost and performance of what they are holding against simpler and cheaper alternatives. The aggregate transfer of wealth from individual investors to the financial services industry through these mechanisms amounts to tens of billions of dollars annually — money that was earned by investors and is being captured by intermediaries who, in many cases, are adding no demonstrable value.

Should I use a financial advisor at all?

The answer depends entirely on which kind. A fee-only fiduciary advisor — one who is compensated exclusively by you, required by law to act in your best interest at all times, and has no financial incentive to recommend one product over another — can add genuine value, particularly in complex tax situations, estate planning, and the behavioral coaching that helps investors stay disciplined through market volatility. A commission-based advisor operating under a suitability standard rather than a fiduciary one is a fundamentally different proposition, because the incentive structures mean that their recommendations are influenced by factors that are not necessarily aligned with your outcomes. The distinction is not subtle — it is the difference between someone working for you and someone working for themselves while appearing to work for you. Asking for the fiduciary commitment in writing is the minimum standard before entrusting anyone with your financial future.

Are index funds really better than actively managed funds?

For most investors, over most time horizons, the evidence strongly favors index funds. The academic and empirical record on active management performance versus passive indexing is one of the most consistent bodies of evidence in financial economics: the majority of actively managed funds underperform their benchmark index over periods of ten years or more, net of fees, and the minority that do outperform in any given period are not reliably identifiable in advance. The implication for ordinary investors is not that active management never adds value — in specific contexts, with specific managers, it can — but that the default assumption should be reversed. The burden of proof belongs on the active strategy, not the passive one, and most of the time that burden is not met.

What should I look for in a financial advisor?

The first and most important filter is the fiduciary standard. Before any conversation about investment strategy, ask whether the advisor is a fiduciary at all times — not just in some advisory capacity but comprehensively — and ask for that commitment in writing. The second filter is compensation structure. Fee-only advisors, paid directly by you as a flat fee, hourly rate, or percentage of assets without commissions or product compensation, have aligned incentives. The third consideration is transparency about cost: any advisor who cannot or will not clearly disclose the total expense ratio of every product in your portfolio, including all embedded fees, is not operating in your interest. These filters will eliminate a significant portion of the financial services industry. What remains is a smaller group of professionals whose business model is actually built around serving you rather than selling to you.