Freud, from The Interpretation of Dreams, ch. 5

The Oedipus Rex is a tragedy of fate; its tragic effect depends on the conflict between the all-powerful will of the gods and the vain efforts of human beings threatened with disaster; resignation to the divine will, and the perception of one's own impotence is the lesson which the deeply moved spectator is supposed to learn from the tragedy. Modern authors have therefore sought to achieve a similar tragic effect by expressing the same conflict in stories of their own invention. But the playgoers have looked on unmoved at the unavailing efforts of guiltless men to avert the fulfilment of curse or oracle; the modern tragedies of destiny have failed of their effect.

If the Oedipus Rex is capable of moving a modern reader or playgoer no less powerfully than it moved the contemporary Greeks, the only possible explanation is that the effect of the Greek tragedy does not depend upon the conflict between fate and human will, but upon the peculiar nature of the material by which this conflict is revealed. There must be a voice within us which is prepared to acknowledge the compelling power of fate in the Oedipus, while we are able to condemn the situations occurring in Die Ahnfrau or other tragedies of fate as arbitrary inventions. And there actually is a motive in the story of King Oedipus which explains the verdict of this inner voice. His fate moves us only because it might have been our own, because the oracle laid upon us before our birth the very curse which rested upon him. It may be that we were all destined to direct our first sexual impulses toward our mothers, and our first impulses of hatred and violence toward our fathers; our dreams convince us that we were. King Oedipus, who slew his father Laius and wedded his mother Jocasta, is nothing more or less than a wish-fulfilment- the fulfilment of the wish of our childhood. But we, more fortunate than he, in so far as we have not become psychoneurotics, have since our childhood succeeded in withdrawing our sexual impulses from our mothers, and in forgetting our jealousy of our fathers. We recoil from the person for whom this primitive wish of our childhood has been fulfilled with all the force of the repression which these wishes have undergone in our minds since childhood. As the poet brings the guilt of Oedipus to light by his investigation, he forces us to become aware of our own inner selves, in which the same impulses are still extant, even though they are suppressed.