There isn't one smart guy or one great strategy - there are dozens of smart guys and loads of strategies and they can win because they outsmart the city types.
As I remember, beaucoup back testing, hilarity ensues anyway.
*edit: I'm not a serious student of this aspect, but I recall that none of the top independent hedge funds took a bath in the 2007+ collapse (that is, those that weren't in-house funds from a major wall st. company). They all had their risk management in order and all did pretty well in buying distressed assets. Some like Bridgewater really managed to grow non-stop right through that.
Coming up with the predictor is often the hard part. For example, take the tweets of a (sane) president and run sentiment analysis on it. If it is positively correlated with mentioning an equity, the sentiment of the tweet might be a good linear predictor of the stock price.
The math is simple once the feature is well defined.
Feature development is the current frontier, as I understand it.