You can use the "[private] tournament winner" selection process up to a certain point, but at some point far below Warren Buffett's current level, you come into the public eye.

If it were akin to flipping coins, we'd almost surely have seen 16+ proto-Buffetts emerge into public consciousness only to see 15 of them blow up. Sure, there have been hedge fund failures and you could argue that Madoff was a public eye super-investor who turned out to fail, but I don't think there are enough examples of "this guy is a genius based on his track record" turning into "that guy we thought was a genius turned out to just be a lucky idiot" to suggest that all of Buffett's returns are luck.