The problem of the silent cemetery(sample bias?). If we start with a large enough cohort of "equally skilled" traders, who just make their investment by random, we will still end up with a handful of "old foxes" who just standing because of their proportional luck. In the meantime the failed ones laying in the cemetery silently as nobody asks them.

Of course the lucky one's skills will be rationalized(narrative fallacy in Taleb's term) and not just by themselves but the majority around them, the media etc..