the best definition of "tilt' i've ever come across is tommy angelo's, which is something to the effect of "tilt is any deviation from A-game performance for any period of time". this is the determining factor. for some people, once they lose 2BI they become frustrated and begin to let emotion influence decisions. for other people, they begin to tilt due to losing concentration after 1hr,1.5hrs,2hrs etc. i personally don't have a set maximum amount of $$ i can lose. but i try to be alert to when running bad/how much i've lost/how long i've been playing are affecting my ability to think clearly and play well, and base my quitting decisions on that.

on the converse. some people (successful players) advocate quitting every time you've lost 3 or 4 buy-ins. this doesn't work for me personally because i try not to look at how much i'm winning or losing AT ALL, especially not while i'm playing (losing) session.