When I was 24, I was just learning to be a trader at Calyon Indosuez. An old French trader told me that the markets have princes but they never have kings. That could mean a lot of things, but what he meant is that nobody's thoughtful enough to make it for long without falling on his face; things change all the time.
I was already a little skeptical by nature, but he convinced me that a lot of the successes you see are just the product of luck. I pushed that to its natural conclusion, which is that most market performance is random.
NEXT: Stick with what you know