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.