My family always used the expression, "scared money never wins". I put an amount of money that I'm willing to lose in my right pocket. At that moment, I consider it gone. I then play at proper limits for my pocket. The money could be used for a tournament buyin, a cash game, or both. I then play my best game. If my pocket is empty in 10 minutes, I go home. I was either dumb or unlucky.
Biggest mistake I've seen is players who want to play for a few hours entertainment and so they chicken to a big bet. They're scared of losing their money too fast.
Kathleen