Index Funds Are Boring on Purpose

The argument for index funds is usually made badly. It is presented as a claim that markets are efficient and prices are always right, which is both contestable and beside the point.

The actual argument is narrower and much harder to dispute: costs are certain and returns are not.

William Sharpe's observation about active management holds regardless of whether markets are efficient, because it is arithmetic rather than economics.

All the shares in a market are held by someone. The passive investors hold their slice at market weight and earn, by construction, the market return minus a very small fee. Everyone else, in aggregate, holds the remaining slice, which is also at market weight. So active investors as a group earn the market return before costs.

After costs, they earn less. There is no arrangement of skill among them that changes the aggregate.

The reason a one percent fee is worse than it sounds is that it is charged on the balance, every year, including on the growth that previous years' fees already reduced.

Figures are rounded and illustrative, and assume a constant 7 percent gross return with no contributions.

The uncomfortable line is the last one. A two percent all-in cost, which is not unusual once a fund fee and an advisory fee are stacked, removes something close to two-fifths of the outcome. It does that without any bad year, any bad decision, or any market event.

“You cannot control returns. You can control costs, and costs compound with the same mathematics.”

The natural response is to pick the funds that have done well. This fails more reliably than intuition suggests.

With enough funds in a market, some produce five strong years by chance alone. Nothing in the record distinguishes those from the genuinely skilled, because both look identical: a good five years. Persistence studies repeatedly find that top-quartile funds in one period are close to randomly distributed across quartiles in the next.

There is also a survivorship problem in the data you see. Funds that perform badly are closed or merged away, so the historical average of the funds still available today is flattering to a category that as a whole did worse.

Here is the part that gets least attention. Studies comparing fund returns to investor returns in the same funds find a persistent gap: the average investor earns less than the fund they were invested in.

The mechanism is not mysterious. Money arrives after good years and leaves after bad ones. The fund's published return assumes you held it the whole time. Very few people did.

Which reframes the entire choice. If the behaviour gap is often larger than the expense ratio, then the most important property of a strategy is not its expected return but whether you will actually stay in it during the twenty months when it is losing money.

• A simple portfolio you understand is easier to hold than a sophisticated one you do not.
• A strategy with no story attached gives you no story to lose faith in.
• Automatic contributions remove the moment where a decision could be made.
• Looking at the balance less often is, unhelpfully, one of the best-evidenced interventions.

The case is not that indexing is clever. It is that it removes three of the four decisions that usually go wrong.

1. Which securities to hold. Removed by construction.
2. Which manager to trust. Removed, along with the selection problem underneath it.
3. What to pay. Reduced to a number you can read before you buy.
4. When to buy and sell. Not removed. This one is still yours, and it is the one that matters most.

Nothing here is an argument that indexing is optimal. A genuinely skilled manager identified in advance beats it. The argument is that the strategy is robust to being wrong about your own skill at identification, which is a property worth more than it looks.

Boring is not a compromise made because the exciting version is unavailable. Boring is the mechanism.