It's really hard to stop someone that tries to recover his losses, even if you stop him his mind keeps telling him to bet more because he can't still accept the reality that his bankroll is gone in just few minutes. Greed is really difficult to overcome because our opponent here is our own emotion. Having a self-control and discipline is also not easy to have. I think most of us experience this in our gambling journey and being an optimist, it taught me a lesson to never chase your losses in gambling. Just exit that casino and relax yourself by doing other stuffs.
I agree, just telling someone to stop will maybe make him stop for an hours or half day. But the losses are always on our head and we keep thinking about how to recover them. If we really want to help someone we need him to fully understand that he is facing the risk to lose even more money. To fully change the mindset a change of scenery could help. Getting out of your own comfort zone can help a lot. So far I always managed to stop myself. Hopefully if it ever gets to far my friends will help me.