I've heard it said that 90% of Americans think that they're smarter than average. I would guess that this is not a deep psychological fact about self-misperception. My theory is that it's caused by two things - the abundance of false praise and those quizzes they show before the movie previews, e.g. "Can you unscramble the name of this star from 'Minority Report': OMT UISCRE?", both of which make people feel smarter than they actually are.