When you hear something you don't want to hear, a magical creature comes out of nowhere, bonks you on the head, and makes you forget what you heard. Then you can pretend you only hear what you want. This process is illustrated below:
Denial is a complex psychological process where there may be some conscious knowledge or awareness of events in the world, but somehow one fails to feel their emotional impact or appreciate their logical consequences.
Denial is an attempt to reject unacceptable feelings, needs, thoughts, wishes--or even a painful external reality might alter our the self-perception or damage our self-esteem. This psychological defense mechanism protects (temporarily, at least) from:
-Knowledge (things we don’t want to know)
-Insight or awareness that threatens our self-esteem; or our mental or physical health; or our security (things we don't want to think about)
-Unacceptable feelings (things we don’t want to feel)
Denial can short-circuit the brain and cause it to malfunction (see this example discussed by David Freddoso)
In other words, it can make you entirely clueless , or even a complete idiot who gleefully enables, encourages, and supports evil.
Needless to say, a mind is a terrible thing to waste.
Sometimes, hearing someone confront those unpleasant truths can be an extremely painful experience, especially when your entire culture is engaged in mass denial, projection and paranoia--all of which lead inevitably to hate, intolerance and bigotry as its defining characteristics.
It's much easier to forget all that unpleasantness. As long as there is someone to blame for your own dysfunction, you can keep on feeling good....for a while, anyway.