Imposing self limits...

[badblood44]

The key here is determining how well or poorly you're playing, not dollars won or lost.

I've heard pros say that they'll play until they feel themselves playing at less than their optimum and that's when they call it a night.

Sure it can be disappointing to lose a buy-in, especially when you feel you're playing some good poker.

Trust me, you can lose a ton playing well and win a ton playing poorly.

Recognizing when your game is faltering is a key factor in determining when to call it quits.