When billions of dollars gush into an ETF that just reported big gains, more gains can soon follow. The problem: The investors themselves are driving those gains—and will suffer when their impact fades.

What your exchange-traded fund owns is important. Who else owns your ETF might be even more important.

That’s because a fund’s returns often don’t depend merely on the behavior of the investments it buys, but also on the behavior of the investors who buy the fund.

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Further reading