Indeed, best to have the fun and not to add more money after losing, those who keep it that way are preventing losing what they can't afford to let go, though there are situation where you wanted to keep trying to win more instead of appreciating the amount that you already won, most of the time chasing for more is harder to resist, as emotion mostly dominates than control your own decision making.
Yes, that's what you have to do, but sometimes we lose control and say, "Let's bet a little more," and we keep gambling, and nothing happens; all we do is lose. I've fallen into that temptation; whenever I should stop betting, I keep betting and I lose. That's something you shouldn't do, but it's really difficult. Now, the best thing you can do is be careful with the money you spend at the casino.