In Oedipus Rex by Sophocles Oedipus the main character Oedipus experiences the life changing event of seeing the oracle and it altered his life in a very negative way.
Oedipus had been living with adoptive parents when he met with the oracle and had been told that he would kill his father and marry his own mother. Hearing this news he fleas his town to avoid his told fate and he ends up running right into his destiny. While at a literal crossroad he faces a quite symbolic crossroads. Deciding what direction he would take determined the outcome of his life. He took the road that was most traveled by and ran into his legitimate father. And killed him.
Seeing the oracle was very significant to Oedipus and had a domino effect and caused many other significant events in his life. He experienced killing his father and marrying his mother. Killing his father in turn sort of guaranteed him marrying his mother.
When Oedipus realized that he had married his mother he went insane. He blinded himself and had a significant downfall.
Going to the oracle essentially ruined his life. By trying to avoid his fate he ran right into his fate told by the oracle.
