It is all good by saying you need to set limits and have discipline but it is sometimes not as easy as that. There will always be moments where you will start tilting and you will be betting higher amounts than usual. Even if you know it is a stupid idea, it is very hard at these moments to be reasonable.
Probably if just new to slot gambling, it will be understandable that he will be having a hard time to set limits on when to stop playing for a while and when to continue. It all depends on the personality and discipline of the player. But I do agree, sometimes, even you're experienced very much, there are times that you can be tilted because of the lose streaks and big losses that you're so you try hard to make it back.
Losing is part of gambling if you make a game. You already enjoy playing, it's hard to pull it out yourself once it entertains you so much, but if you lose a lot of play, this has an impact on the emotional, physical and mental state of the gambler that might urge towards to play more to get their wins back. Always gamble responsibly because the gambling platform does theirs, and the players are responsible for their gambling habits.