The trick is that any non-illegal investing strategy has finite potential, because it is exploiting some sort of mispricing by the market. Eventually either your buying and selling will correct the mispricing, or other investors will catch on and start doing the same thing, spreading the profits thinner among a larger crowd.

This means that if you want to continually beat the market, using any strategy beyond an impressive gut, you need to be continually developing new tricks and strategies, finding new market mispricings to exploit as your old ones dry up. It's like juggling: someone who is skilled or lucky can keep the balls in the air for quite a bit of time, but eventually you're going to run out of tricks, and the best you can hope for when that happens is returning to average returns.