[Harv72b]

I try not to limit myself based on the number of BBs I lose (or win) in a session, but one of my criteria for quitting has always been "if I'm not playing well". You're a winning hold'em player because you make better decisions than your opponents do--if a few bad beats or a run of bad cards puts you on tilt and takes away that edge, you are no longer a winning player. As such, you should quit playing until you have calmed down enough to get your edge back.

I tend to think that you can recognize when you're tilting and making bad decisions, and that you don't need to tie it to some magical number of BBs lost. Just play your game, and whenever you can't play your game, for whatever reason, stop playing.