One of the key aspects of tragedy in Aristotle's understanding of the term was the way that it linked in with hamartia, or a personal flaw in the tragic hero, which was responsible in part for the tragic downfall of that character. In so many cases, that tragic flaw was the result of hubris, or excessive arrogance, which led to the tragic downfall. Oedipus is of course at the beginning of the play something of a hero. He has saved Thebes from the ravages of the Sphinx and as a result has been given both the crown and the queen to take as his wife, Jocasta. His arrogance is clear in the way he responds to the news that the way to cleanse Thebes is to track down the killer of Laius, the former king, and punish him:
Now you have me to fight for you, you'll see:
I am the land's avenger by all rights,
And Apollo's champion too.
Oedipus clearly has incredible faith in his own abilities, and this is again indicated when Jocasta persuades him, temporarily at least, to ignore the prophecies of the gods and to try and cheat fate. The key hamartia, or flaw, of Oedipus, is the way that he feels he is not subject to fate in the same way that other characters are because of his heroic nature. This is the key of the tragedy in this powerful play.