Wealth disparities will always exist as long as information takes time to distribute and is not public. This is, I think, what the GP means when an "average investor" thinks he has information or a system that the market doesn't and trades on it. If that trade succeeds, it reinforces his behavior. If it fails, something else must have gone wrong but he keeps letting his system drive his money until he can't take the losses (or he makes a bunch of large trades successfully and quickly retires).

It's the equivalent of poking the market with a stick with a pavlovian response when there's several academic fields that would explain a great amount for you instead (which was expensive before the internet).