Actively managed funds underperform their benchmarks more often than not over long periods. The reasons are structural rather than a reflection of individual competence.
The arithmetic of the average
All investors in a market collectively hold the market, so the average dollar invested must earn the market return before costs are deducted.
Active managers trade against one another, and one manager's outperformance is another's shortfall. The group cannot collectively beat the average it forms.
Once fees are subtracted from that average, the typical actively managed dollar necessarily returns less than the index it is measured against.
Costs compound against the manager
Management fees are charged on assets regardless of performance, so a fund must beat its benchmark by at least its fee before a client sees any advantage.
Trading itself carries cost beyond commission. Every purchase crosses a spread, and large orders move prices against the buyer while they are being filled.
These costs recur annually while the benchmark carries none, so the required margin of skill is a hurdle that resets every year.
Size works against the strategy
Success attracts money, and a larger fund can no longer take meaningful positions in smaller companies without owning an impractical share of them.
The manager is pushed toward larger, heavily researched companies where an informational edge is hardest to find, which is exactly where the benchmark already concentrates.
A strategy that worked at modest scale can therefore stop working precisely because it worked, without anything about the manager having changed.
Returns are concentrated in few holdings
Long-run market returns are driven by a small minority of companies producing extraordinary gains, while a large share of listed firms underperform cash over their lifetimes.
A concentrated portfolio that happens to exclude those few winners will trail badly, even if every other selection was reasonable.
An index fund holds them automatically, which removes an entire category of error rather than solving it through judgement.
Why persistence is hard to identify
Distinguishing skill from chance requires a long record, because short-term results contain enough randomness to make a lucky manager and a skilled one look identical.
By the time a record is long enough to be informative, the manager may have changed, the fund may have grown, or the conditions that suited the approach may have passed.
This is why past performance is a weaker guide than its prominence in marketing suggests, and why costs remain the most reliable predictor available.