I know that as gamblers, everyone can relate to this question, as we have surely experienced it in real situations.
Suppose our bankroll is $100 and it has already grown to $500, would you quit or continue? Conversely, if with our bankroll, we are down to $10, would you still continue or save the remaining $10? I used specific amounts to make it easier to discuss this situation. I understand that we all gamble with different amounts based on our income, but consider this as an example. You can mention any amount you want based on your personal experience; it doesn't matter.
Personally I had a set target both when winning or losing I quit, however before I reached that conclusion it took me a while to achieve it, from my past experience in gambling I was find it difficult to quit after some losing streak until the fund is gone because I usually experience some urge to continue gambling probably I may breakeven unfortunately ended up losing all, while I find it easy to quit after some winning streaks because I always withdraw all my profits earned, meanwhile I believe other gamblers find it difficult to quit after some winning streaks and after a loss, now I am more disciplined, manage and control my gambling habit.