When you no longer have fun when you play, just take a break to start fresh later. Gambling is a game that is meant to entertain us. If you see it as a business that can be profitable, you're doing it wrong. You should stop when it's starting to affect your financial situation.
For me, gambling is all about fun. Once you loose that, it's time to rest and a break can be good.
People will find it hard to have fun anymore when they faced a bad result (lose) and unfortunately at such situation, people tend to forget their previous plans regarding gambling. People will keep chasing their previous lost instead of stopping at that point.
I think everyone does have a hard time when they are feeling negative in a way. It's hard to know what to do in those certain situations but one thing is for sure is that if you are gambling with profit in mind and not planning for the future games, you would lose your money. That's my opinion on it but who knows maybe luck would be there for you.