In seeking resolution, our primary goal is to preserve our sense of self-value

When we join a health club that is too far away, we may justify the purchase by telling our friends that the workouts are so intense we only need to go once a week; when we fail to get the grade we’d like in organic chemistry, we tell ourselves that we didn’t really didn’t want to go to medical school anyway. But there is another aspect of cognitive dissonance that should not be underestimated, which is that such “irrational” tendencies tend to be reinforced when we are surrounded by others who believe the same thing we do. If just one person had believed in the “doomsday cult” perhaps he or she would have committed suicide or gone into hiding. But when a mistaken belief is shared by others, sometimes even the most incredible errors can be rationalized.

From How Cognitive Bias Can Explain Post-Truth