Even if "you" (who/what is "you" by the way?) do understand the principle "you" have mentioned, the mind will experience cognitive dissonance. It can't be avoided as it happens on a layer below conscious perception.
"You" seem to think that beliefs exist on a conscious self-aware layer of thought, thus "you" should be aware of them but if "you" have done any serious psychonautics or experienced traumatic events in childhood, "you" will realize that is not the case. It takes a lot more than simple affirmation to rid "yourself" of such demons. Reading books about ceremonial magick and the techniques that had to be invented over the years to deal with such problems can be very enlightening, if not fascinating.
So, when the mind experiences cognitive dissonance, the effects propagate to the upper layers and "you" may become aware of them. I guess my point (through experience) is that as long as there is a "you" there to begin with, cognitive dissonance and dissociation will be problems that "you" will have to deal with :-)
As to your original question, it has long been my view that "most people" are not self-aware enough for such matters to even register. Even those who do have the curiosity and inclination, don't really like spending a lot of time in that UNCOMFORTABLE space, and quickly reach for the nearest distraction or escape (living in a make-believe dream world) to help them cope with daily life. When the luster starts to fade, a new dream bubble (new goals and aspirations) is quickly conjured and entered.
I highly recommend Celia Green's "The Human Evasion" [1] to you, something tells me you will enjoy it very much.
[1] http://deoxy.org/evasion/