definitions of delusion:
(psychology) an erroneous belief that is held in the face of evidence to the contrary
a false belief, seen most often in psychosis (for example --- schizophrenia)
a groundless, irrational belief or thought, usually of grandeur or persecution; generally a characteristic of paranoia
definition of myth:
traditional story accepted as history; serves to explain the world view of a people
a common story or legend. Although the word "myth" means untrue to some people, to others it embodies a different kind of "truth" which expresses their deepest and truest values, fears, hopes, and beliefs.
Like allegory, myth usually is symbolic and extensive, including an entire work of
any "story that teaches". The story need not be "true" or historically accurate, but is designed to teach moral lessons.
a story that expresses a spiritual truth or basic conviction of a culture through narrative.