From Aristotle, Jedi Master:
But when one takes a larger look at the story of Anakin Skywalker’s fall, one sees a special genius at work in the creation of that story.And no, the genius in question is not George Lucas. Lucas succeeded in following the rules and using the elements of classical tragedy to tell the story of how Anakin Skywalker became Darth Vader. But those rules and elements were themselves laid down for posterity a long time ago, in a country relatively far away.
It was Aristotle in his Poetics who discussed the construction of the tragic drama. Aristotle notes that the fortunes of the tragic hero must swing ‘from happiness to misery; and the cause of it must not lie in any depravity, but in some great error on his part…’ Tragic fear and pity, on the part of the audience, ‘may be aroused by the Spectacle … he who simply hears the account of [the tragedy] shall be filled with horror and pity at the incidents…’ Thus, the tragic hero must have a fatal flaw, or ‘some great error’ that helps arouse ‘horror and pity’ on the part of the audience.