For me it's the most important thing! It doesn't really matter how good you are at poker, if you can't control your mind you will be ruined as a player.. you gotta learn to control your emotions... Otherwise poker won't work that well for you
Its realy hard for me when I dont believe someone have the hand which is drew on the table. lol I always think the other one is lying. Self control is life!
I think it's one of the most important things to become a good poker player. If you let your emotion affect you and you lost your control you will make many mistakes. And if there is a thing more important than self-control, I think it is studying, your knowledge about poker. You can not play well if you just have a little understanding of poker, especially modern poker. Top players even have to review their hands with others. So I always read books or watch analyzing from pro players to improve my play when I have time.