As the questions says, when do you stop? your point of no return?
a. at least double your money, then stop
b. you only stop when you have lost all your bankroll money and then blame the casino?
c. or you are a superstitions gambler, when you have signs like losing 3 straight in a row, then you quit because you know that you're having a bad luck
d. you stop when you are at least break even
I didn't include chasing your losses as obviously you might to continue.
My limit is when I have lost my bankroll, this is is a sign for me to quit because if I don't it's going to end in disaster. I always have a fixed for the month and once it's completely exhausted I just stop immediately because at that point my emotions might make me start thinking of touching the money in my Bank account to start chasing my losses. This is a limit that I don't break and it has helped to keep me in check