Thus, Teiresias, although verbally abused by Oedipus, at first protects Oedipus from this self-knowledge with a reflection on the brutality and horror that can come from wisdom:
Alas, how terrible is wisdom
when it brings no profit to the man that's wise!
This I knew well, but had forgotten it,
else I would not have come here. (Oedipus the King 316-9; trans. David
In fact, many people in Thebes already know who Oedipus is, know his true origins, but refuse to tell him. In addition to Teiresias, it appears to Jocasta (Oedipus' mother/wife) figures it out very quickly and tries to protect her husband/son from this terrible self-knowledge, and, finally, the shepherd who took Oedipus as a baby knew all along and thought it best not to tell.
After his self-realization, Jocasta commits suicide and Oedipus blinds himself with her brooch. But he says something else quite interesting. He says:
It was Apollo, friends, Apollo,
that brought this bitter bitterness, my sorrows to completion.
But the hand that struck me
was none but my own. (Oedipus the King 1329-33)
There is much going on here. Something to do with the original oracles that the child would kill his father resonates. But I think closer at hand was the oracle at the beginning of the play that set Oedipus to discover WHO in fact killed the previous king of Thebes, Laius, whom he fails to realize was his own father. It was this oracle that forced him on a pursuit of knowledge that would be his downfall. Indeed, as I paraphrase Ecclesiastes, whoever increases knowledge, increases sorrow. But there is something else here too. The gates to Delphi said, "Know Thyself." It is by setting events so that Oedipus would come to know himself that Apollo sent him bitter bitterness. In all of this, trapped by these events of which he is simultaneously guilty and innocent, his self-blinding becomes an event in which he has total control. It is a means to reassert his free will against fate.