http://en.wikipedia.org/wiki/Black_Monday_(1987)
That unpredicted event made him and his organization loads of money, and made him a sudden seer of markets. Which is humorous because his book Fooled By Randomness is primarily a bit of a bitter tirade about how we declare people savants because they happened to be in the right place at the right time.
Since then he gets the classic seer type treatment, for instance the other post notes that he "predicted" the financial collapse of 2008 (weird that someone would register just to post that). Yet almost everyone predicted 2008. No, seriously, the house bubble and crisis, and the probable impact on the market, was absolutely common knowledge by the time Taleb made his pronouncements, and was the endless material of virtually every financial discussion. There was absolutely nothing of worth predicted in that, but that's what you get when you got lucky once.