And even with high volumes, you can always pick something retrospectively that beats the market. It's not useful to look back and say, for example, if you put money into X stock at Y time you'd beat the market. You can't go back in time so it's not useful.

What is useful is to figure out what, today, may predict outperformance tomorrow. In choosing fund managers, it's not enough to choose managers who've outperformed in the past - that's not in itself predictive of the future (same is true for home prices as we learned in 2008, individual stocks, etc.). But other characteristics might be predictive, like choosing fund managers who follow a true "value" approach to stock-picking: finding companies with a competitive advantage and buying them below their intrinsic value being one approach to value.

See Warren Buffett's 1984 article "The Superinvestors of Graham and Doddsville" for the best example I know of distinguishing chance price rises from predictable rises: https://www8.gsb.columbia.edu/articles/columbia-business/sup...