If you dont have discipline then most likely you will fail.
Discipline has no link to gambling.
you don't gamble with discipline. That would mean you intend to have a strategy and to win.
You can't have a strategy. it's useless.
Gambling is for the fun of it! For the thrills and how you wish to hit that button again
Maybe what he means is the discipline to stop when he is losing a lot, people tend to continue in the hope that they can regain what they've lost and it's true you must know when it's to admit that you've lost and come back the other day to try to regain your losses, not try to regain your losses when you are losing badly.