alt Hacker Newsfor the last one, that's the whole story of Socrates being the wisest man because unlike others he knew the bounds of his knowledge:
"I seem, then, in just this little thing to be wiser than this man at any rate, that what I do not know I do not think I know either."
For those interested, it’s not just in Apology this comes up. In Theaetetus he does a pretty good job disproving that it is even possible to know what knowledge is.