I would agree that hubris or pride is Oedipus's one tragic flaw.
The key to Oedipus's tragic downfall is not simply that he is proud and believes he is an exceptional person, although that is an element of his personality. The Greeks, as we do today, did not have a problem with people having a positive self image. Oedipus' tragic hubris is his belief he can beat the gods. This is a chief sin in the Greek worldview.
The gods have ordained that Oedipus is destined to kill his father and marry his mother. However, when Oedipus learns this is his fate, he tries to circumvent it by leaving the people he believes are his parents. He flees his home, taking the road from Corinth to Thebes to escape his fate, but ironically, it is his very attempt to "win" out over the gods by leaving Corinth that leads him straight into the arms of his destiny. On the road, he meets and kills a man who won't step aside to let him pass, unknowingly murdering his real father. Arriving in Thebes, he then marries...
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