But it's an equilibrium, right?
No, why would it be?
Equilibrium is a convenient mapping tool that lets you assume away a lot of difficult issues. Reality is not in equilibrium.
Because when it's easy to outguess the market, the people who are good at it get richer and invest more money in it until it gets hard again.
It's not in perfect equilibrium constantly. I've heard of someone working out some new method that made it easy which took off over the course of a few years until enough people used it that outguessing the market was hard again.
Another month, another rationality quotes thread. The rules are: