You are very right about this.
* Stop when you have a big winning, by channeling the money somewhere else so you won't lose it back to gambling.
I do not know what you mean by big winning because most gamblers can not win up to that. But it is good to stop even if it is small winning already. Continuing gambling will only later likely lead to losses.
* Stop when you are not even winning at all, it's not your thing.
I do not think this is possible. If you do not have fun while gambling without thinking of the money to win, then it is not your thing. If you gamble with small amount of money many times, you will win and also lose. But if you win more than losing in some few gambling time, then it is good to stop.