What causes us to have illusions/fantasies?

Is every thought believed? Why do we create our own illusions/fantasies? Just because we do not believe in our present reality or a circumstance we create our own illusionary reality...why? I that a rational excuse of our human nature? pljames

I am writing an article on this and I will let you know when it is finished.

If you want an idea look up the god gene

Bruce Hood argues in his book "SuperSense" that the belief in fantasies (religion, magic, superstitions, cognitive biases, etc) is hard wired into the brain.

Considering belief in one form or another of illusion is practically omnipresent in humans, that sounds quite plausible.

I would put a link to the book, but the forum won't let me...