Really dumb people don't know that they are really dumb. Dumb people know that they are dumb. Below average people think they are average. Average people think they are smart. Smart people know they are smart but not highly intelligent. Highly intelligent people think they are geniuses (including in all possible fields). Geniuses, real honest-to-goodness geniuses, know that they are smart in many ways but mostly dumb.

I cannot prove it, but this is how I think it is. For the record, I think I am smart; however, because of the Iron Rule of Intelligence above, it is equally possible that I am only average.