I know I know nothing.
I am sure some people see this as a contradiction, or even as a negative proof, prooving that knowledge does not exist at all.
I say it is possible to see it the other way around. That the assertion of knowledge is more solid than our concept of "nothing" (as being negative).
It is especialy appropriate for Socrates, given his method, that "nothing" not be something negative at all, but that it is actually something neutral. That it is the state of ignorance within which the meeting of minds can actualy take place, and then generate the form of co-investigation for which Socrates is known.