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.