I have often said in the past:
You have to know what you don’t know.
Often my test of a good manager or developer is to query to find out if they know what they don’t know. If they have no idea — if they can’t shape out or draw a box around what they don’t know — then that’s not a good thing in my book.
I was talking to a colleague of mine, Greg Della-Croce, and he said:
You have to first know that you don’t know.
He’s absolutely right.