Oedipus Rex's tragic flaw is his hubris, or excessive pride. He believes that he is better than everyone else because he answered the riddle of the Sphinx, became King of Thebes, and saved the city. Now that the new curse is upon the city, Oedipus believes he is the man to find the killer of the previous King. Not realizing that his own father was the previous King and that this is the man he killed years before, he boldly and openly promises to bring the murderer to justice. He has plenty of warnings from gods and Terisias, the blind prophet, but ignores them all, because he wants to be the hero again. This arrogant promise to find the murderer and break the city's curse leads to his downfall because he is successful in all of his stubborness. He does find the murderer - himself! It is at this point that his life falls apart; his wife (and mother) commits suicide, he blinds himself, and his children are horrified. If he had listened to the warnings, he would have never known. Ignorance can be bliss!
Hubris is a technical legal term in Greek meaning something close to aggravated assault (specifically, a form of violence which is also an insult). Pride leads people, according to one theory of tragedy, to commit hubris.
The popular culture misuse of the term stems from a misreading of Kitto's book on Greek tragedy. Misusing the term this way is a sign of having read a limited amount of secondary literature but not actually knowing Greek (it is often accompanied by the even worse barbarism "the hoi poilloi").
Oedipus's flaw is said to be hubris. While the Greek word hubris is generally translated as pride, a better understanding of it suggests the relationship between humankind and the Pantheon (the gods). The concept that hubris describes is actually that of forgetting humankind's position in relation to the gods: humans are weak and limited while the gods are mighty and powerful.
Accordingly, Oedipus's flaw is that, being wise and powerful in his own right, he puts his trust in human knowledge and ability. This is a sort of pride, but pride in humanity rather than personal vain pride. This is born out when Oedipus berates and mistreats Teiresias, who is called the "voice of Apollo," as he rejects what Teiresias says to him.
OEDIPUS:Do you really think you can just speak out,
You most disgraceful of disgraceful men!
You’d move something made of stone to rage!
say things like this, and still remain unpunished?
So, Oedipus's basic flaw is hubris, which according to some is personal pride but according to other scholars is pride in humanity that supersedes acknowledgment of the gods' might. In other words, he tries to outsmart the prophecy for his destiny and in so doing thus becomes subject to the retribution the gods, or fate, hand down upon him.
Alas, alas! How dreadful it can be
to have wisdom when it brings no benefit
to the man possessing it. ....
What’s wrong? You’ve come, but seem so sad.
Let me go home. You must bear your burden
to the very end, ....