After you've had success in the valley, people are willing to fling money at you for just about anything.

This factor alone accounts for a large percentage of repeat successes. Square probably never would have obtained the capital necessary to become competitive, had it not been for Twitter.

But honestly, for all their funding, even most of these second tries turn out to be failures. What you're really doing here is confusing selection bias with skill: take a pool of enough entrepreneurs, and eventually, just by chance, you'll find someone who has repeat successes.