There's this bit in Taleb's first book, "Fooled by Randomness". This was before he made a shit-ton of money. He pointed out that a lot of the nominally successful traders he worked around would declare a strategy, make a few bets, make a lot of money, and then act like geniuses for thinking up the strategy. However, they'd never really examine the obvious alternate hypothesis: they got lucky.

I used to work for a proprietary trading firm. We'd get new traders by taking very confident, driven people (e.g., former Olympic athletes), making them be clerks for a while, and then turning them loose in the pits. The CFO kept a very close eye on them early on because their natural confidence combined with early successes lead them to believe they were gods. It wasn't until they got really hammered by a bad bet or two that she'd begin to trust them.

It reminds me of a favorite line: "Every corpse on Mount Everest was once a highly motivated person with a can do-attitude."