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Oedipus caused his own downfall because of his pride. He did not listen to Teiresias who warned him to not investigate Laius's death. Oedipus was too stubborn however, and continued on. This is a common theme in a lot of Aristotle like tragedies. Another argument could be made that Oedipus causes his own downfall simply because he doesn't know who he is. If anything, he was ignorant during his actions, while he was trying to uncover the past.
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Do you mean you'd like references?
Here is an example:
Relating to Oedipus and his downfall resulting from not knowing who he was: Oedipus is described many, many times and wanting to "see". His curiousity in this case is not a vice, simply who he is because he doesn't know his past. This helps contribute to his downfall.
Is that what you had in mind?
Well, I don't have the play in front of me, and I think that is a little more than I want to chew off right now. I'll opt out of this question and give other Experts the chance to answer. They can work with what I already started for you.