Even if he already lost before, that will not stop him from gambling especially if he become emotional. Gambling can make he forget with his loss without think about stop gambling.
His regret will only happen for a while and that will not make him really realize that he lose his money. If he can introspect about the impact that he get, he will really regret and do not want to have the same thing again.
For a moment of adrenaline rush, we forget a lot of things. I have seen countless times people suggesting that you should have a limit in losses, you should control your emotions etc etc. Even I did. But at the end of the day, how many of us are able to follow these advices? IMO, the majority of us cannot. The heat of the moment, the intense pressure makes us numb. We cannot make practical decisions or assess the situation in these moments, which leads to massive financial losses.
You will not be able to have self control over your gambling activities when you are after making profits. This is why some people finds it difficult to stop the game, despite the fact that they are running at loss because they can't let go of their losses. I have been in a situation of gambling and losing but I couldn't stop till my bankroll was empty. Let's not allow our emotion to control us when gambling.