Thinking you know too much is the correct expression. There is this story about a student who solved a previously unsolvable math problem because he didn't know

Thinking you know too much is the correct expression. There is this story about a student who solved a previously unsolvable math problem because he didn't know it was unsolvable (http://www.snopes.com/college/homework/unsolvable.asp http://www.snopes.com/college/homework/unsolvable.asp). If you believe to know the limits of what is possible, you will hold yourself back. For the beginner, everything is possible. I think that's a wonderful message.