Knowledge is encoded in models. Models are synthetic sets of rules, and pictures, and algorithms providing us with useful representations of the worl… - Didier Sornette

The old Wall Street saying " buy on rumors, sell on the news," is alive and well, as can be seen from numerous sources in the media and the Internet. Rumors can drive herding behavior strongly.

Positive feedbacks, when unchecked, can produce runaways until the deviation from equilibrium is so large that other effects can be abruptly triggered and lead to ruptures and crashes.

Profiting from being in the minority leads to interesting paradoxes. Rather diabolically, if all traders use the same set of rules, they will end up doing the same thing at the same time and cannot therefore be in the minority.