It is easy to say but hard to implement. I have tried to control my betting size as well as time of the session. But with time and at some point everything fails.
Everything fails only because you are not determined enough to control it and do what you set from the beginning. You are the main reason that it all failed. If you are determined enough to stick to the plan than that wont happen. Even if it does happen then the chances for it to ruin yourself should be low enough
You are correct, but I understand that it's hard to do that, at least in the beginning. I would suggest that he, or anyone in his situation, would just try to do some "paper gambling". I know it might sound stupid, but it's not. If you are not risking any money, and just simulating bets, then you have nothing to lose and can keep calm and test some gambling strategies. In the long run you can see if it works or not. If it does, then you have built some confidence and will probably continue to remain calm when you are making real bets.