Here's a step-by-step breakdown of how Oedipus comes to this realization:
1. The Arrival of Teiresias: Oedipus summons the blind prophet Teiresias to inquire about the identity of the person responsible for the plague in Thebes. Teiresias is reluctant to reveal the truth, but eventually hints that Oedipus himself is the cause of the city's suffering.
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2. Accusations and Doubts: Oedipus becomes suspicious and accuses Creon, his brother-in-law, of plotting against him. He also questions the credibility of Teiresias, leading to a heated confrontation.
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3. Quest for the Truth: Despite his resistance, Oedipus is compelled to seek the truth. He interviews various characters, including Jocasta and the herdsman who saved him as a baby, to piece together the puzzle of his past.
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4. The Revelation: As Oedipus delves deeper into his history, he encounters more evidence pointing to his tragic fate. He learns that he was abandoned as a baby due to a prophecy foretelling his actions, and he begins to suspect that he may be the one responsible for the oracle's predictions.
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5. The Final Truth: Finally, Oedipus confronts Jocasta and uncovers the shocking truth. Jocasta reveals that Oedipus is indeed her son, and she confirms the horrifying details of his past. Overwhelmed by guilt and shame, Jocasta takes her own life.
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6. Oedipus's Downfall: Oedipus is devastated by the revelation. He realizes that he has unwittingly fulfilled the prophecy and brought calamity upon himself and his family. In a state of despair, he blinds himself and leaves Thebes as an exile, forever carrying the burden of his tragic fate.
Therefore, at the climax of the story, Oedipus comes to the horrifying realization that he is the unwitting perpetrator of his own tragic destiny, marked by parricide and incest, leading to his downfall and banishment from Thebes.