There is only one thing which causes a Myth and it is the accretion of unproven and at times unprovable but palatable and sweetened facts. A Myth is probably a historical figure, who though accretion of eulogy and mindless belief on the merits of the facts narrated by the previous generation, becomes an irreplicable (just coined a word) symbol of some quality or power!
A Myth is something which lacks a counterpoint ! There should be nothing required to complement it in any way.
In the process the society hates any negative input to those characters except the wicked and evil ones. There is no blend, there is no internal jostling, just peaceful harmony.
The casualty in all this Myth making is the Seeker of Truth! He has no incentive for ascertaining the Truth and declaring it. Thereby becomes a rare breed taking private tuitions like Aristotle to Alexander because of the munificence of his father Philip of Macedonia! When the Truth seeker becomes a private tutor he becomes a mercenary of knowledge, when he is idle, he becomes a cynic- like Diogenes!
An evolved culture is one when negative comments are allowed to co-exist without any pressure from the majority and judged by the law and the Justices under a common law.
Now do we know why we Indians are excellent mythmakers? Anyone can add to the image so long as it is a positive comment eulogising the object! There would be no touchstone in that culture which will come to value copper as much as gold all for want of TOUCHSTONE! It is in that touchstone lies the value of the metal!