Self control is just something else that we talk about almost all the time but not all gamblers take that very seriously as it appears hard for them to follow, I’m happy to see that in your last statement you said “don’t be too greedy” which show acknowledging that gamblers are always greedy in nature it’s just a matter of how much you can control that greed.
We say a lot of things to others like do this, do that, avoid this, ignore that and so on. But when it comes to applying the same rule in our own life, most of the times, we cannot or unable to do so. It's somehow similar with gambling. Some may say, we must control our emotions, keep them in check but in reality it's a lot harder than you think. Like the old saying, "it's easier said than done". When adrenaline kicks in, things like self control doesn't works. And before you realize it you are already ruined.
If I say about my point of view, I would say "time" plays a crucial role here more than anything. A person cannot just self taught themselves to control their emotions in a night. It takes a lot of patience and time to get rid of the addiction and control their play.
This is 100% true, really, even though we can give advice to others, it becomes very difficult to apply it in our own lives, especially when bad things like emotions and addictions are involved. Not everyone has the ability to control themselves, especially when it comes to gambling. No one can get out of gambling addiction just by wanting to, because its addiction is so terrible that even if the gambler wants to stay away from gambling, he will not be able to stay away from gambling because of this addiction. Because the thing is that this addiction controls the gambler's mind.
Getting out of gambling addiction is not impossible, just like you said, it takes patience and time to get rid of this addiction. Yes, if the gambler gradually reduces the amount of gambling, then at some point this addiction will completely end. But for this, it is necessary to have willpower.