In "Oedipus the King," does pride or fate bring Oedipus to his downfall, and could he have done anything different to have a happy ending?

I believe that Oedipus' downfall is dictated by fate. I do
 not believe that his pride is at fault, and I do not belief he could have done things
differently to exact a better outcome.

In terms of the
question of Oedipus' fate, a prediction was made about what would happen to Oedipus, so
if one is to believe in predictions, he had no control. However, it does not stop his
parents from trying. He is abandoned by his parents on a hillside to starve with the
hope of thwarting the prophecy. Oedipus is saved and raised in another royal household.
Hearing of he prophecy, he leaves his adopted home to protect his "father" (not knowing
he is adopted), only to meet his real father on his way and kill
him.

A terrible monster called the Sphinx kills all passing
travelers who cannot answer his riddle. Oedipus does this, and defeat the Sphinx so that
travelers may safely move about. Oedipus is brought as a hero into the city of Thebes
(where he was born, though he does not know this). There he is given in marriage to a
widow as a reward: however, the woman is his mother, and so the prophecy is
fulfilled.

Sophocles and his culture (the Greeks) believed
in predestination: that your life was mapped out for you before you were born, and that
nothing could be done to change the fate the gods had in store for
you.

In this case, Oedipus tries to do
the right thing, which immediately puts him in the position of not
protecting his [adoptive] father as he had hoped, but killing his
real father and marrying his
mother.

There was nothing Oedipus could do to provide
himself with a happy ending.