The Myth Ledger · Myth 04 · Base-rate neglect
“Index funds settle for average returns.”
A low-cost index earns the market before tiny costs; the average active dollar earns the same market before larger costs, while the average fund also risks missing the few giant winners.
What survives scrutiny
“Average” quietly changes denominator. An index is average across invested dollars before costs—not average among high-fee funds after costs. Because stock outcomes are strongly right-skewed, broad ownership also solves a discovery problem: no one knows in advance which small set of companies will create most aggregate wealth.
Evidence stack
What the literature can—and cannot—say
Tags distinguish measured evidence, economic foundations, model-dependent results, and important limits.
Economic foundation
Active management is zero-sum before costs, negative-sum after costs.9
For every active overweight there is an offsetting underweight held by someone else. In aggregate, active investors hold the market. Higher research, trading, distribution, and advisory costs then lower the aggregate net result.
Empirical evidence
A few stocks do extraordinary work.10
The distribution of lifetime stock outcomes is highly skewed. Broad indexes continuously include emerging winners; concentrated selection creates a material risk of excluding the companies that dominate wealth creation.
Empirical evidence
Skill is hard to distinguish from the tail luck creates.11,12
Fund studies and scorecards repeatedly find widespread net underperformance and weak persistence. Factor exposure, benchmark choice, category changes, and style drift complicate attribution; even so, a prior winning rank alone is not a durable selection rule.
Technical lens
The fee is a hurdle, every year.
If two portfolios own equivalent risks but one costs an extra percentage point, the active portfolio must generate that much gross alpha merely to tie. Compounding turns a modest annual hurdle into a large terminal-wealth gap.
net active return = market return + gross alpha − total cost
Concrete example
The index does not need to identify tomorrow’s champion.
A selector must both own the rare outsized winner and size it enough to matter—without concentrating disastrously in false positives. A broad index accepts many mediocre holdings as the admission price for never deliberately excluding the unknown tail winner.
Decision checklist
A decision rule, not a slogan
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- Use low-cost, broad, rules-based funds as the default core.
- Compare any active proposal with the correct benchmark after every layer of fee and tax.
- Write the falsifiable reason the manager should have an edge, why it should persist, and who is on the other side.
- If keeping an active sleeve, cap it at a size that cannot impair the plan and track dollar-weighted results.
Optional lab: explore the assumptions
The default illustration is readable without JavaScript. Changing its inputs requires JavaScript; outputs are not forecasts.
Counterfactual lab · illustrative
The active hurdle
Give two strategies the same gross return and expose what the higher-cost strategy must overcome before skill reaches the investor.
Index wealth
$1.8M
Active wealth
$1.3M
Fee gap
$416.6K
The active strategy needs roughly 1.2% of repeatable annual gross alpha just to erase the stated fee difference—before tax, turnover, and selection mistakes.
Open the full fee paper →Model boundary · $100,000 initial balance, $10,000 annual contribution, annual compounding, constant gross return and fees; tax and trading impact omitted.
Chapter sources: evidence and limits
Original source numbers are retained across chapters. Each finding travels with its limitation.
- 9The Arithmetic of Active Management ↗
Sharpe, W. F. (1991). Financial Analysts Journal 47(1), 7–9.
Finding: Before costs, the aggregate active dollar must equal the market; after higher costs, the aggregate active dollar must lag it.
Limit: The identity applies to a properly defined market and aggregate holdings, not to a claim that no active investor can outperform.
- 10Do Stocks Outperform Treasury Bills? ↗
Bessembinder, H. (2018). Journal of Financial Economics 129(3), 440–457.
Finding: Long-run wealth creation in U.S. equities is extremely concentrated in a small minority of stocks.
Limit: The comparison is buy-and-hold to bills and the result does not mean most stocks always fall or that concentration can be forecast in advance.
- 11Luck versus Skill in the Cross-Section of Mutual Fund Returns ↗
Fama, E. F. & French, K. R. (2010). The Journal of Finance 65(5), 1915–1947.
Finding: The distribution of mutual-fund performance is largely consistent with insufficient net alpha after costs, with few extreme outcomes beyond chance.
Limit: Factor models are imperfect and the study does not say skilled managers cannot exist; it says identifying them ex ante is hard.
- 12SPIVA U.S. Scorecard, Year-End 2025 ↗
S&P Dow Jones Indices (2026). S&P Indices Versus Active scorecard.
Finding: The recurring scorecard compares active funds with category benchmarks across horizons and reports survivorship and style consistency.
Limit: Results vary by category and period; benchmark choice, taxes, and investor-specific constraints can change the relevant comparison.