It gets easier and easier to beat the market (due to less people trying) until eventually investors can make enough money doing that to earn the fees they charg

It gets easier and easier to beat the market (due to less people trying) until eventually investors can make enough money doing that to earn the fees they charge for trying. There's an equilibrium when that happens. EDIT: Or, to put it in EHM analogy terms, the number of people looking for loose change on the sidewalk will go down until there are few enough to support themselves from the money people actually drop.