Socrates believed that no one does wrong voluntarily. Evil is the result of ignorance. If people knew what was the right thing to do they would do it. We always choose what we think is the best or good for us.
Socrates always claimed that he did not know anything; this resonates the essence of what Socrates is about. Wisdom is a sort of recognition of your own ignorance, thus Socrates knows that he is not wise; therefore he has a type of wisdom.