Greed is what makes a gambler to continue gambling despite even starting his whole gambling session with an ideal target or time he would want to gamble but at his playing everything changes in a split second when the urge to gather more comes into his taught and I doubt that he would even remember even setting boundaries because that quest to acquire more overshadows every other taught in his head and that what's make him lose everything too at the end and then starts chasing previous which can turn him to an addicted gambler.
This can happen if the gambler has no discipline. Even you already set a budget to use for playing, it will be useless if you don't have discipline. Unable to control your emotion is indeed a problem of a gambler because you'll tend to forget your main plan before deciding to play the specific game.
It's a human nature to be greedy sometimes, but it's a must that you can still think of what should be the right thing do, is it to go beyond your limit or stick to your set plan? If you chose the latter then you're a kind of gambler who never let greed influence you just because you are winning/losing.