I only play slots and after 30 minutes i usually get bored no matter if Ioosing or winning. However 30 minutes could have a huge effect your balance if you play volatile slots 
It's the same with the normal slots depending on your desire if you're wanting to bet more or not. As you've said, after 30 minutes, you easily get bored and you might tried to find other games that will remove your boredom. It depends on how active you are but most gamblers that do get bored easily, they won't stop. They won't even cash out so it's a question that we all can answer ourselves because it'll depend on how much it is in our balance but sometimes even if it's a lot already ,we won't withdraw it.Yeah it's our own decision making and like what you said even how decent the amount we already have we still trying to push for it and aim to win more, it's about how good you are in controlling yourself, though most of the time it's greed and too much excitement that lead a gambler to continue instead of cashing out and enjoy whatever the earnings that he already gain from the game that he's playing.