Perhaps the most significant threat to taking us off the path of having the proper mind set is the element of frustration. As an obvious example, we're all familiar with the player "on tilt," and probably have experienced it ourselves to various degrees over the course of our poker playing careers. The analogy of being on tilt in fact comes from pinball machines, where often the player becomes frustrated and shakes the machine too violently, causing it to stop functioning properly. This is a very good analogy in fact as this is pretty much what happens at the poker table as well when players let frustration get the best of them and allow it to reign over them. Their game immediately stops functioning properly, usually adding liberally to the loss which prompted the anger.
While this is the obvious version of allowing frustration to get the best of us, there are more subtle variations that can occur as well, not putting us on tilt so much as taking us off our game to one degree or another. And any instance of allowing frustration to pollute our play is an instance which it's important to avoid. We already need to worry about opponents and bad luck swings beating us out of our money, but when we add to the situation by beating ourselves out of money, we now have a serious matter and one that needs to be addressed, regardless of the degree.
I'm pretty sure we're not all Buddhist Monks though as far as having control over our emotions, and I'm pretty sure we wouldn't want that sort of control anyway. This would take a lot of fun out of the game, as aside from the money we may make, there's a lot to be said about the satisfaction, even exhilaration that comes from succeeding. And if we're going to get emotional in a good way, we of course run the risk of getting emotional in a bad way as well.
Having said that, most of what causes us to be frustrated arises purely out of misunderstanding. Sure, it's probably normal to get a little disappointed at least when our set of aces lose to a garbage hand hitting perfect perfect on the turn and river. Disappointed perhaps, but not necessarily upset, very upset, or even enraged. We may even compound the problem by telling our opponent just what kind of a moron he really is for playing his hand that way. This way we not only give him our money but a free lesson as well. One of my pet peeves is when these players either insult or try to educate the fish at the table when this stuff happens. I want to tell them to shut the &*#$ up in fact :), as we don't want them to change a thing. In fact I'll usually congratulate the dummy for his nice hand, as I really would like him to continue his horrible play, and certainly don't want to discourage him in any way, and especially upset and insult him and perhaps have him leave the game.
A lot of the problem that arises within us here stems from the fact many players feel at least somewhat entitled to win a hand if they are ahead in it prior to all the cards being dealt, and particularly if they are ahead by a significant degree. As a general rule though we want people to stay in the hand with us when we have the advantage over them, and don't mind their risking their money in situations which we're favored to win in the long run. In doing so though there's always the potential for other players to beat us.
If we are a 2 to 1 favorite over a player, for instance, out of every 3 instances we'll beat him 2 times and he'll beat us once. Those are pretty good odds of course and our expected value here is going to be 1/3 of a pot each time we play this. Naturally though the opponent will win 1 of the 3 times - he's entitled to that, as even bad odds are entitled to hit, just as our good odds are. We must understand this though and not get upset as this profitable process unfolds. And we must especially not look to take it out on the opponent, as if we would prefer him not getting involved in these profitable situations with us, or there be two dummies involved here and not just one.
What emerges here, in order to best seek to remedy this problem, is the need to focus on playing the odds correctly rather than just focusing on isolated permutations of them. Unless we have the absolute nuts, we're never entitled to win a given instance, no matter how high the odds are in our favor or how badly our opponents play. In other words, we keep our focus on playing correctly and let Lady Luck do her own thing, knowing with absolute mathematical certainty that by doing so we will get the best of it. And it doesn't matter how forsaken we may feel at times by her, the laws of probability remain steadfast by our side, assuring us our due in the end.
Whether you let yourself become a little frustrated, go on a rampage, or anything in between, it is critical in fact that we look to develop our understanding of this process. In seeking to master this, we significantly increase our chances of success, and by the same token, by allowing these misunderstandings of the laws of probability to diminish our game, we significantly diminish our chances accordingly. By tending to our own play, and letting the odds tend to themselves, we'll be assuring that the odds will always run with us over time.