this usually happen when you lose money, lose too much , have high hopes of winning. no one wants to lose so its not bad to feel remorseful after that. when this repeats itself too often then it can mean that such person is not gambling responsibly. its good not to gamble with any money you cant afford to lose. this is easier said but might be difficult that is why you should set aside a percentage of your income for gambling like 5% and never go beyond that.
Every gambler suffers from regret when he loses a bet. Especially when a big bet is lost due to a mistake, regret is high in this case. Emotions are always at work in humans but if they are under control then there will be less regrets. There are some gamblers who bet a certain amount and can control themselves from excessive greed, for them, even if they lose in gambling, there is less regret. In contrast, gambling regrets are high for those who cannot control or use any necessary money to gamble. Above all, if we expect less from gambling and use it as a temporary enjoyment, losing in gambling will not be regrettable.