The time to quit gambling is before you start.
I disagree, but oh well, I have gambled before, so I guess that is the gambler speaking.
Gambling is a negative EV activity. Therefore the highest EV is 0 with 0 wagered.
This unless you call Poker gambling like some people seem to do. Then it will totally depend on your skill and emotional stability.
Well, I have made quite a lot playing Roulette. I always withdraw my initial deposit as soon as I win something. That way I won't lose it. Also I withdraw a part of my winnings every time I hit a certain threshold, plus I stop playing when I hit a streak or lose twice.
Because of all those things I have made quite a buck, but most people just crack and try to get their losses back, which result in more losses.