In his fifth-century BCE tragic play Oedipus Rex, Sophocles explores issues of free will, fate, and the consequences of intentional ignorance.

At the appearance in the play of Oedipus's wife, Jocasta, the audience learns the prophecy of Oedipus's fate that relates to the death of her husband, Laius, the former King of Thebes. It's very likely that most of the people who attended the performance of Oedipus Rex at the Festival of Dionysus in 429 BC already knew the story of the play from the Oedipus myths and legends they had heard from childhood, but Jocasta repeats it for dramatic purposes and for later audiences unfamiliar with the story..

JOCASTA. An oracle
Once came to Laius...declaring he was doomed
To perish by the hand of his own son,
A child that should be born to him by me. [...]
As for the child, it was but three days old,
When Laius, its ankles pierced and pinned
Together, gave it to be cast away
By others on the trackless mountain side.
So then Apollo brought it not to pass
The child should be his father's murderer,
Or the dread terror find accomplishment,
And Laius be slain by his own son.

Oedipus cannot escape or in any way change his predetermined fate. No matter what he or anybody else does, Oedipus will kill his father and marry his mother, and he did.

King Laius, Oedipus's father, was far more concerned with his own life than with Oedipus's life when he ordered a shepherd to take the baby Oedipus into the mountains and leave him there to die. Laius's actions didn't alter Oedipus's fate in any way.

When Oedipus heard the same prophecy from the Oracle when he was living as the son of King Polybus and Queen Merope in Corinth after being saved from death in the mountains, he decided not to return home to Corinth in order to avoid the prophecy. Nevertheless, Oedipus fulfilled the prophecy when he killed Laius on his way from the Oracle to Thebes.

Free will seems to exist in the ancient Greek world to the extent that the day-to-day decisions that a character like Oedipus makes are essentially unimportant and inconsequential. The gods are far more concerned with the major, life-changing events in Oedipus's life. They have better things to do than decide what Oedipus is going to have for breakfast or which sandals he's going to wear.

Laius and Oedipus can do whatever they choose to try to avoid Oedipus's fate, but their free will choices to avoid Oedipus's fate don't make any difference.

Sophocles also explores the consequences of intentional ignorance. At the opening of the play, Oedipus is truly ignorant of some important events in his life—being taken to the mountains to die, being adopted by Polybus and Merope—and he's also ignorant of the importance of events of which he is aware.

As the play continues, and as facts and circumstances begin to point to Oedipus as Laius's murderer, Oedipus becomes resistant to this new knowledge and closes his mind to it. Even in the face of overwhelming evidence, Oedipus repeatedly denies that he is the man who killed Laius and thrust Thebes into the depths of blight and plague. The facts are there, but Oedipus refuses to acknowledge or accept them.

There's no immediate consequence of this intentional ignorance for Oedipus himself—he'll eventually come to know and accept the truth of the matter—but the consequence for the people of Thebes is that their suffering due to the blight and plague is unnecessarily prolonged.

Oedipus is enabled in his intentional ignorance by Jocasta. Early in the play, Creon tells Oedipus that Laius was murdered by a band of robbers.

CREON. Robbers, he [the survivor] told us, not one bandit but
A troop of knaves, attacked and murdered him.

In the same speech cited above, Jocasta refers to the report of the survivor of Oedipus's deadly encounter with Laius that "so at least report affirmed," Laius "was murdered on a day by highwaymen."

Later in the same scene she reinforces this point.

OEDIPUS. In thy report of what the herdsman said
Laius was slain by robbers; now if he
Still speaks of robbers, not a robber, I
Slew him not; "one" with "many" cannot square.
But if he says one lonely wayfarer,
The last link wanting to my guilt is forged.

JOCASTA. Well, rest assured, his tale ran thus at first,
Nor can he now retract what then he said;
Not I alone but all our townsfolk heard it.

Eventually, Oedipus and Jocasta suffer the consequences of their intentional ignorance. Jocasta kills herself in shame and grief, and Oedipus blinds himself with the gold pins in Jocasta's robe when he discovers her body.