Both Oedipus and Achilles live by the universal code of human assertiveness and free will, even though each of these characters is foretold of a horrible fate that lies in store for him.
Achilles, for example, is warned that if he goes to fight at Troy, he will lose his life. He will gain the glory he desires, but with glory comes death. Still, he chooses to assert his own will to achieve his desire of respect and honor.
Oedipus is warned of a horrible prophecy, one that involves killing his own father and sleeping with and impregnating his own mother. Rather than hide away and cower from life, Oedipus goes on to assert his greatness by solving the riddle of the Sphinx and saving the city of Thebes. He goes on to become their king and gains the utmost admiration from his role in guiding his people.
In the end, both characters do meet their destined ends, but their courage in the face of such tragic circumstances is something to be admired.