Why

A person who believes they are telling the truth even though the objective evidence strongly supports the claim that they are lying is deceiving themselves into believing the lie because they desire the results. A belief so motivated is usually considered more flawed than one due to lack of ability to evaluate evidence properly. The former is considered to be a kind of moral flaw, a kind of dishonesty, and irrational. The latter is considered to be a matter of fate: some people are just not gifted enough to make proper inferences from the data of perception and experience.