If you're trying to locate them after the fact it's quite easy, nothing hard about it at all. It's using skill to identify them before any given period that's

If you're trying to locate them after the fact it's quite easy, nothing hard about it at all. It's using skill to identify them before any given period that's hard. Plenty of people do in fact end up identifying them before any given period, but no more than would be predicted by chance, so it is quite hard to prove that anyone at all identifies outperformers using skill; it's laws of chance at work, even though many like to think they used skill (or like for you to believe they used skill, if they're trying to get you to pay them to manage your money).