Tragedy of Oedipus is about pre-destination vs free-will. Fate does play a part in the tragic down fall of Oedipus but it does not mean that his character and disposition has no liability for that. Excessive arrogance and self-confidence of Oedipus is the main cause of his tragedy. He harbors unjustified suspicions against Tiresias and Creon; in one place he goes so far as to express some uncertainty about the prophetic natures of oracles and truth of their prophecies.
It is hardly likely that even a combination of all these would be equal to what Aristotle considered to be a serious hamartia, and it would not be very relevant to the point at issue even if he did, for Oedipus has committed incest and parricide years before the action of the play began, and before he exhibited any of the failing mentioned above. It would hardly be logical to say that the gods punished Oedipus for a crime which he was to commit many days later.
Another view is that the present failings of Oedipus may be taken to means that he was he was always like that, and his tragedy comes due some inherent or innate unsoundness in his character. So he is not a puppet in the hands of fate. But Sophocles also illustrates that it was fate that brought him to Thebes and it was gain fate that he came across someone at where three highways came together.
It was his fate that he married his mother. Above all, fate has played a pivotal role in his life from the very start and has not dealt with him even-handedly. The divine will as predicted and proclaimed by the oracle was absolute and it has nothing good about Oedipus. Although certain measures were taken by the King and Queen) to escape from that proclaimed destiny but it became the cause for the tragic downfall of Oedipus.
That is the reason that Oedipus says after blinding himself. God. God. / Is there a sorrow greater? /Where shall I find harbor in this world? / My voice is hurled far on a dark wind. / What has God done to me? (Sophocles 831) Dodds writes about the nature of fate as demonstrated by Oedipus that fate is “inevitably and inexorably bound to happen no matter what Oedipus may have done to avoid it (Dodds 21).