People can't give up the flattering self-illusion that they can just tell when someone is lying. That they can read someone's character. Admitting that you can't really read people makes the world a scarier place.

I mean, Ann Rule was a former police officer and later a crime writer. She worked with Ted Bundy on a suicide hotline, and had no idea. You really can't read people. It's just in the movies where the bad person just looks and sounds shifty.