It's very hard as from time to time there are changes with your adrenaline and you keep pushing and trying to win more which being produce by your emotions, without a good control on it, the chance of losing more would be be the outome of your session, better to pause for a while and stop your gambling session, assess yourself instead of keep trying to win back.
Taking a break and stopping the gambling session is what he should do immediately before all his money is wasted on gambling, and he will regret seeing it. However, it is difficult to stop immediately after experiencing a losing streak, and it takes time to master self-control. But if he is willing to learn it and practice it, he can stop gambling immediately and even leave gambling immediately after he experiences a loss or win. He will feel he is better off stopping for a moment and leaving gambling than he will repeat the same mistakes he has experienced before. That's where he can learn from his experience and will not repeat it because it really makes him experience even more losses.