One key lesson is to acknowledge the complexity of the world and resist the impression that you easily understand it. People are too quick to accept conventional wisdom, because it sounds basically true and it tends to be reinforced by both their peers and opinion leaders, many of whom have never looked at whether the facts support the received wisdom. It's a basic fact of life that many things "everybody knows" turn out to be wrong.

How could an investor use that? The uncertainty involved in predicting complex events would argue for some level of diversification and a greater focus on hedging. At the same time, the fact that people tend toward overconfidence and follow conventional wisdom should provide opportunity for those taking contrarian positions against that. The trick, of course, is to have concrete justification for why the crowd is wrong.

—Robert Shiller