first, a definition:
Cognitive dissonance is a psychological phenomenon which refers to the discomfort felt at a discrepancy between what you already know or believe, and new information or interpretation. It therefore occurs when there is a need to accommodate new ideas, and it may be necessary for it to develop so that we become “open” to them.
now the post from ars teholigica
Let me offer an example. Suppose you are told that a certain book contained no errors whatsoever, and that it was perfect and infallible in every way. So naturally you placed your complete trust in this book, and lived according to its wisdom, and all was well. Then along comes some new knowledge, irrefutable facts which contradict the teaching(s) of this book. You experience dissonance, and since dissonance is unpleasant, even traumatic, you must find a way to reconcile the knowledge of the book with the new information.