Play great defense

The most imporatnt rule of trading is to play great defense, not great offense. Every day, I assume every position I have is wrong. I know where my stop risk points are going to be. I do that so I can define my maximum possible drawdown. Hopefully, I spend the rest of the day enjoying positions that are going in my direction.

source: Paul Tuodr Jones in Market Wizards, J.D.Schwager