That experience will haunt them even while they're sleeping lol.
I've been in a similar position. The regret of winning when you already had your winnings but couldn't cash them out.
But now, that experience reminds me that even small wins are meaningful and can be enjoyed. There's no need to be greedy and keep playing, aiming for bigger wins. Greed in gambling is indeed disruptive, gamblers must learn to control it.
Almost every gambler has had the same experience. There is always this feeling that you can win more if you take greater risks. But we still have to acknowledge that the bigger the risk the higher the chances of winning big. So we shouldn't feel bad when we lose all because we failed to cash out. Celebrated gamblers are high-risk takers.
But just like most people have commented, our greed level should be controlled to avoid regrets. Currently, I have decided that I will cash out of any game that I suspect might be unfavourable. I am not taking much risk anymore because small wins can help me recover some of my losses.