See also, the work of Robert Trivers [0] on the evolutionary utility of strategic self-deception. Sometimes we deceive ourselves so we may more effectively deceive others (or more charitably, perhaps to signal in-group loyalty).

Ironically enough, I think this can even take the form of an irrational belief that humans are innately rational, when empirical observation tells us otherwise.

[0] https://en.wikipedia.org/wiki/The_Folly_of_Fools