A lot of wisdom in this excerpt from Mobs, Messiahs, and Markets: Surviving the Public Spectacle in Finance and Politics:
… if there is one thing we know about the sentiments of crowds, it is that they change. Today it is greed. Tomorrow it is fear. But rarely is it doubt. So, when mass sentiment goes negative, it goes completely negative. People stop worrying about the return on their money and begin to be concerned with the return of their money.