A single behavior in the first five years of investing often explains why index funds underperform an investor's expectation: people stop feeding them. They buy an S&P 500 fund, survive a correction, see paper losses and then pause contributions or sell. The result is not a market failure; it is a compounding failure.
Put another way: the math of compounding rewards uninterrupted inputs more than it rewards short-term timing. Miss the early habit of regular contributions and dividend reinvestment, let taxes and fees nibble at returns, and even the market's long-run edge won’t make you rich.
Here is a concrete example. Two investors, identical except for one choice. Both start with nothing, both commit to 6000 dollars a year in a plain total stock market index fund. Investor A contributes 6000 dollars every year for 30 years. Investor B makes the same 6000 dollars contribution for five years and then stops, letting that pot ride for 25 years with no new money.
Assume a 7 percent annual return before fees and taxes, a reasonable long-term equity assumption. After five years, both have about 34,500 dollars. If Investor A keeps contributing, after 30 years the portfolio will be roughly 567,000 dollars. If Investor B stops after year five and makes no more contributions, the portfolio grows to roughly 187,000 dollars. The difference—about 380,000 dollars—exists purely because of ongoing contributions, not because one investor picked a better fund.
That gap is what I call the compounding error: treating an index fund as a static asset you can pause funding to, rather than as a machine that needs continuous fuel. The first years of a plan are where habits form. Stop the habit, and you stop the engine.
Two mechanics explain why pausing contributions is so destructive. First, contributions are additive while returns are multiplicative. Each new deposit buys shares that compound on future returns. Early deposits compound the longest, but regular deposits across decades matter more than any single early or late contribution.
Second, behavioral pain is frontloaded. New investors see volatility, they feel losses, and they react. The market, though, does its wealth-building over long stretches and often concentrates upside in a surprisingly small number of days or months. Missing those upswing periods because you exited, or missing years of compounding because you stopped contributing, costs far more than most people realize.
In plain numbers: continuing 6000 dollars a year for 30 years at 7 percent yields roughly 567,000 dollars. Stopping after five years yields roughly 187,000 dollars. Same returns, different behavior, three hundred eighty thousand dollars in difference.
That is not theoretical. Employers find that new 401(k) participants who automate contributions and keep them in place are far more likely to reach retirement balances that matter. Automation reduces the chance that you will sell or pause during a downturn; it forces you to benefit from future rebounds without having to predict them.
Behavior is the largest drag, but fees and taxes quietly compound damage. Expense ratios look small—0.05 percent versus 0.60 percent—but over decades those decimals widen into tens of thousands of dollars. If gross market returns are 7 percent and your fund charges 0.60 percent instead of 0.05 percent, the net annual return drops to about 6.45 percent. Compound that over 30 years and you end up with roughly 13 percent less wealth than the low-cost investor.
Taxes do the same work. A taxable account that distributes dividends and realizes capital gains each year forces you to pay money that would otherwise compound. Consider a normal taxable portfolio that produces a 2 percent dividend yield and trades enough to generate realized gains taxed at 15 percent. The tax drag can reduce your effective annual return by 0.3 to 0.6 percentage points, enough to shrink long-term outcomes materially.
Asset location—what you put in a tax-advantaged account versus a taxable account—matters. Bonds and high-dividend strategies are usually best kept inside 401(k)s and IRAs where taxes are deferred. Low-turnover index funds and ETFs that produce qualified dividends are more efficient in taxable accounts. Use the account structure to protect the compounding engine.
Sequence-of-returns risk is usually discussed as a retirement problem: a market crash in the first years of retirement requires selling into losses. The same logic applies for new investors who stop contributing. If your early returns are negative and you react by stopping contributions, you lock in a poor sequence. Even identical average returns over long spans can deliver dramatically different outcomes depending on timing and contribution discipline.
Here is a short, simple rule: you want negative returns early only if you are contributing aggressively at the same time. Each purchase in a dip gets cheaper shares and larger future compounding. If you instead freeze purchases, you convert temporary paper losses into permanent opportunity costs.
You do not need better predictions. You need a plan that makes compounding automatic and shields it from bite-sized human impulses.
First, automate contributions at a level you can sustain. Even 1 percent of salary invested automatically beats sporadic lump sums. Automation enforces consistency across market cycles and eliminates the temptation to pause after a downturn.
Second, prioritize tax-advantaged accounts until you hit the match and a reasonable contribution target. Employer matches are literally free money, and tax-advantaged growth magnifies compounding. If you have a choice between a taxable account and a 401(k) that offers a match, take the match every time.
Third, cut fees. Replace expensive active funds with broad market index funds that charge a few basis points rather than hundreds. Expenses compound too. John Bogle called this the arithmetic of investment expenses; even small differences persist and amplify over decades. For a strong primer on the math of fees, Vanguard’s paper on investment expenses is still worth reading at the source.
Fourth, be deliberate about asset location. Put bond-like strategies and active, high-turnover funds inside tax-deferred shells. Keep tax-efficient, low-turnover index funds in taxable accounts where they can benefit from preferential long-term rates and tax-loss harvesting.
Finally, reinvest dividends. If your platform offers automatic dividend reinvestment, use it. Dividends are a raw, reliable source of compounding. When they are paid out and left idle, they interrupt the geometric growth your plan depends on.
Panic is a human reaction; it is not an investment strategy. When markets fall, the correct program is the opposite of what panic urges: keep contributing or, better yet, increase contributions if you can. Lower prices mean more shares for the same dollars, which is how compounding accelerates.
If you cannot increase contributions, at least maintain them. If you have a taxable emergency fund, keep it separate from your investment account so you are not forced to sell equities during a downturn. Treat the first five years as a runway where discipline compounds faster than market timing.
If you want reading that reinforces this idea with historical data, Vanguard’s work on time in the market explains why staying invested beats trying to pick highs and lows. The numbers make this plain: missing a few of the market's best days can drastically cut lifetime returns, and those best days often follow the worst days.
Ignore the siren song of short-term performance. Your index fund is doing its job. Your behavior might not be.
The title of this piece sounds accusatory because it must. Index funds do not make you rich on autopilot. They create the conditions for wealth—low fees, broad diversification, efficient exposure to growth—but you still have to fuel the engine. The most costly choice is the passive one: to stop contributing because the account shows a loss you feel in your gut but not yet in your long-term balance.
Fix the habit. Automate contributions. Use the right accounts. Cut fees. Reinvest dividends. Those are not glamorous prescriptions. They are arithmetic. They will not guarantee wealth, but they will restore the compounding that index funds promise and most investors unknowingly sabotage in the first five years.
Change those behaviors now, and decades from now you will find that the market did most of the heavy lifting—because you finally let compounding do what it does best.
