Cognitive dissonance. Anyone who aims to be a great thinker needs to understand this concept. It is one of the primary drivers of self-deception. Cognitive dissonance is the name given to the feeling produced when the brain tries to hold two conflicting ideas as true at the same time. There are many of our beliefs which contradict each other, because it is an impossible task for our brains to compare every single one of our beliefs with every other one for consistency. However, the brain likes consistency, because any inconsistency would suggest that the mental narrative in your head that you use to explain the world and your place in it is flawed. So when our brain discovers or is presented with conflicting beliefs, it feels uncomfortable. There is a need to reduce this feeling akin to the need to reduce the feeling of hunger or thirst. And our brains, ever valuing efficiency, seek to do this easiest way possible, which usually means lying to itself.
An obvious example of conflicting beliefs is that the world is only 6000 years old, yet evolution has happened over millions of years. Both of these things can't be true. If you already believed the earth is young, then evolution means your worldview is wrong. That doesn't feel good. There are two ways to reduce that bad feeling. We can accept the evidence for evolution and substantially change what we thought we knew, and possibly a little bit of who we thought we were, or we can find a way to reject evolution. Obviously one of those things is very hard, and one is very easy. Guess which one the brain prefers. The brain is inclined to take the easy route, and it comes equipped with an array of tools and mechanisms to help it reject information is doesn't like, while the skills needed to analyze and accept evidence must be learned and cultivated.
The more a belief is ingrained into our thinking or tied to our identity, the harder cognitive dissonance will work to conserve the narrative. Nevertheless, cognitive dissonance is there to dictate much lesser conflicts as well. It's always lurking, waiting to coddle you, to fend off your insecurities, and to justify your decisions. It's capable of affecting not only your decision making, but your perceptions, your actions, your judgments, and even your memories. The truth is you could not function without it - there would be no way to make sense of the world. That doesn't mean, however, that you should embrace it.
If you want to delve into the subject, I recommend a book called Mistakes Were Made, But Not By Me, By Carol Tavris.
