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.

> If it was purely based on luck, without any talent involved, you'd expect billion dollar companies to be more evenly distributed, and not cluster among certain individuals.

I agree with you that talent is a thing. That said, the Matthew effect is also a thing. Winning tends to compound – partially because talented people are repeatedly successful, but even lucky untalented people can be repeatedly successful because of all the attention they get.

The example that's coming to my mind now is a little silly but – there are lots of funny people on Twitter who barely get any retweets, and there are moderately funny things said by popular people on Twitter who get tonnes of retweets and responses suggesting that they're the funniest people ever.

It takes a lot of work and/or luck (probably usually both) to get to the point where people just lap up everything you say, but once you're there, there IS a certain Halo effect of sorts.

Sorry if not water-tight, just rambling here

Would you? You'd expect a bell curve; a small number of complete failures of entrepreneurs, lots of moderate but eventually failed attempts, lots of moderate but somewhat successful businessmen, and a couple of repeatedly successful ones. You got three. And all that's compounded by the way that success in one business, even if it was purely by luck, drastically increases the likelihood of success in another simply by giving you more capital. How successful has Elon Musk been? He started one reasonably successful company, then got in early at a very successful one, and has been using the capital from those ventures to fund interesting projects--but as cool as Tesla and Spacex are, I wouldn't call them wins yet.

In the long run, luck and genius are probably both necessary but not sufficient; I have no doubt that Zuckerberg's a very smart guy, I just think there are many, many people just as smart who aren't billionaires.