We really have to try to be responsible gamblers to have good self-control to avoid all the bad things that might come to us while gambling. When we can gamble casually, and there is no burden to try to win, we can get a win, like you said. But of course, after we get a win, we don't need to keep trying to get other wins that might be more difficult to obtain.
So it's okay if we fail to win at gambling, and that could be because we are out of luck in getting the win. One day, we will be able to get even more wins, so we will be happier to see those wins. The important thing is that we can continue to enjoy gambling as we should and not lose more money.
back to human nature to always be dissatisfied or greedy with what they got right away even with a $20 budget getting a $100 win is a huge amount but some gamblers feel themselves lucky and continue betting to earn a little more. however, as I said, everything returns to the principles of each gambler and one of the best ways is to only gamble responsibly.
failing to get a big win or a small win is not a problem for me because of the way gambling works to benefit the gambling owner and lets just say that if the defeat helps to provide funds to develop the gambling business.

Always.
It's hard to make oneself think that it is enough. It is sufficient for withdrawal. There will always be that part of our brain that wants more.
I have been in this position a lot of times. I gained 10 fold of my balance and yet I am still there trying to increase it to 20. But as soon as I saw my balance kept on going down after hitting the 10 fold. It made sense that it might be the limit I could get so I need to withdraw if I can make it happen again.
Luckily, I did and 3 days ago I withdrew a chunk of the amount and left a little bit for more playing time.
Discipline is a thing that is hard to apply. There will always be greed, envy from other gamblers winning more, and the thought that maybe we are lucky that day. All this considered, it becomes harder to let go or withdraw.