One’s cocksureness is in proportion to one’s unconsciousness; the more unconscious one is, the more is one sure of oneself. The most foolish are always the most vain. Your stupidity is in proportion to your vanity. The more one knows… In fact, there is a time when one is quite convinced that one knows nothing at all. There’s not a moment in the world which does not bring something new, for the world is perpetually growing. If one is conscious of that, one has always something new to learn. But one can become conscious of it only gradually. One’s conviction that one knows is in direct proportion to one’s ignorance and stupidity.
Ref : Questions and Answers 1953