Self-deception

Self-deception is a process of denying or rationalizing away the relevance, significance, or importance of opposing evidence and logical argument.

It has been argued that humans are without exception highly susceptible to self-deception, as everyone has emotional attachments to beliefs, which in some cases may be irrational. Some evolutionary biologists, such as Robert Trivers, have even suggested that, because deception is such an important part of human behaviour (and animal behaviour generally), an instinct for self-deception can give a person a selective advantage: if someone can believe his or her own "lie" (i.e., their presentation that is biased toward their own self-interest), the theory goes, he or she will consequently be better able to persuade others of its "truth."

This notion is based on the following logic. In humans, awareness of the fact that one is acting deceptively often leads to tell-tale signs of deception. Therefore, if self-deception enables someone to believe their distortions, she will not present such signs of deception and will therefore appear to be telling the truth.

It may also be argued that the ability to deceive, or self-deceive, is not the selected trait but a by-product of a more primary trait that is selected. Abstract thinking allows many evolutionary advantages such as more flexible, adaptive behaviors and innovation. Since a lie is an abstraction, the mental process of creating a lie can only occur in animals with enough brain complexity to permit abstract thinking.