If eight or ten people place their hands on your head and push you down, your knees will buckle, no matter how strong your are. The crowd may be stupid, but it is stronger than you. Crowds have the power to create trends. Never buck a trend. If the trend is up, you should only buy or stand aside. Never sell short because “the prices are too high” — never argue with the crowd. You do not have to run with the crowd — but you should never run against it.
Respect the strength of the crowd — but do not fear it. Crowds are powerful, but primitive, their behavior simple and repetitive. A trader who thinks for himself can take money from crowd members.
– Alexander Elder, Trading for a Living