Basically we've tackled this in our circle of friends. Mostly, they are gamblers, but their answer is quite simple. as long as you haven't lose amount of your total amount of fund you've bet, you could try to play again and again. Once it exceed your investment or total bet, it is pretty fair to stop it right there, and go back when you have another set of funds to risk and play again. But in my opinion, I need to have almost 5 times of profit first from playing because IMO, it is not worthy to stop if you haven't earned allot.
A gambler will not stop his game by just having a target money to obtain, if he will gonna do this one, it will only makes him frustrated and will keep him anxious and the tendency of it is it will make him addict, let the gambler to enjoy his game, but in moderation and proper management of time and especially money. I will not stop gambling since it is my hobby and it makes me feel happy.