Dunning-Kruger effect

An interesting read. "The unskilled suffer from illusory superiority, rating their ability as above average, much higher than it actually is, while the highly skilled underrate their own abilities, suffering from illusory inferiority."

http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

Another homorous way of saying this is that if you are an optimist, then you don't have all of the information.