How does Oedipus's ignorance lead to his blindness to truth?Oedipus Rex by Sophocles
Oedipus's ignorance, or lack of knowledge, leads to his blindness to the truth in Thebes because of the irony of his having solved the riddle of the Sphinx. For, since he has been clever enough to effect the destruction of the Sphinx, in his pride, or hubris, Oedipus believes that he is superior in intellect to others and he has been made king of Thebes where he marries Jocasta.
In his pride and self-assuredness, Oedipus places a curse upon the man responsible for the plague:
I pray that that man's life be consumed in evil and wretchedness
And as for me, this curse applies no less.
And, when Teiresias tries to be discreet about informing Oedipus that he is the perpetrator of the crime, the king becomes angry, charging the priest that if he had eyes, he would be the one who has committed the act. Teiresias responds,
I say that you are the murderer whom you seek...
I say you live in hideous shame with those
Most dear to you. You can not see the evil.
In his pride, too, Oedipus thinks that Kreon is envious of his position as king and calls for his death; nevertheless, he is not completely responsible for his ignorance of the truth. For, Teiresias speaks in what Oedipus calls "infantile riddles"; the shepherd cannot be forced to speak until his life is at stake, and Jocasta certainly seeks to shelter her husband/son from the truth. Finally, Oedipus believes that he is control of his life, but fate has intervened with his ignorance of Jocasta as his mother and the man whom he murdered as his father. His arrogance and pride have, as the Chorus declares in Ode 2
Tempt[ed] and outrage[d] God's holy law;
And any mortal who dares hold
No immortal Power in awe
Will be caught up in a net of pain;
The price for which his levity is sold.
Pride, confidence that he is superior in intellect and can defeat fate, knowledge withheld by the shepherd and Jocasta--all of these contribute to Oedipus's ignorance and blindness to the truth.
Ignorance means want of knowledge but also mistake, misunderstanding (OED). So, Oedipus's fatal mistake is assuredly his conspicuous lack of understanding of human relationships since he is afforded with the possibility to escape his fate several times - to no avail.
He is impervious to the other characters' desire 'not to know' or to have him stay ignorant of the truth for his own sake. He may be devoted to Thebes until the end, and yet, he is utterly inefficient and bitter.
The tragic ending brings about the catharsis and the purgation of passions but there's room for doubt: didn't he all bring it himself merely by forcing the other charactes to talk. Indeed, the etymology of the word "fate" is "that which cannot be spoken".