I think that you missed interpersonal skills. The longer I play poker the more I understand that what Brunson and all those pros mean when they say that poker is a game of people. In fact, most of my decisions in the game don't have anything at all to do with my cards per se. They have more to do with my opponents. My though processs begins and ends with "Why would he do this action now?" In sum, I think that your statement that there are only a limited number of decisions to make assumes a very narrow understanding of the number of decisions that actually have to be made. Sure, at any given time you only have to decide whether to check, bet, raise, or fold. But the action that you take happens within the context of a myriad of other decisions, and those other decisions have to do with your conception of your opponent. Further, I think the elements of the game discussed in the other posts are secondary to your interpersonal skills. Discipline is important because you must fold when beat. But how do you know you are beat? Because you understand your opponents.