most of us act irrationally most of the time but come up with rational excuses to justify it after the fact.

this is absolutely true, and a great point. I played poker professionally for many years, and also coached aspiring poker players.

Because poker is a discipline where, in individual cases, the correct play does not necessarily lead to a desirable outcome, the tendency to play poorly based on emotion or boredom, then rationalize the play after the fact is a huge impediment to novice players. In fact, there are many people i have found who simply can't learn from their mistakes in poker, because their ability to rationalize is just so well honed that they can justify any play they make by tweaking opponent ranges.

Its also true that an objective set of standards it a great protection against this sort of rationalization. But it is not the only protection. One can make an effort to approach certain matters rationally, instead of emotionally. It requires a very conscious decision to recognize your emotion, and not permit it to influence your decisions.