It needs practice and real discipline, let's be honest that it's one of the hardest thing to do, once we enjoy gambling we are forgetting about this especially when we are winning, we think that it's our day and we keep playing and playing until we lose. Player needs to know its limitation and starting to practice it from time to time is a great start in my opinion.
Yes, discipline is easy to say but not easy to practice, even if you realize it. I've experienced this when I was betting on poker and I realized about discipline, initially playing with complete control to occasionally take a break when betting even though it was a win. But in the end I felt if I continued that I might get bigger wins, so I lost in a very short time. So yes, discipline is only easy as a theory, because in reality if we still can't control our passions then we will still be trapped in defeat and that is also a sign that you are addicted because you will be obsessed with taking back what has been lost.