Neat-o psych effect
Found this while looking for something else. It's a Psychology thing, called the Dunning-Kruger effect.
Basically, people who aren't very skilled at something over-estimate how good they are (relative to other people), because they don't understand the activity enough to know how much they suck.
Meanwhile, people who are skilled tend to under-estimate their abilities -- because they think that other people find the task as easy as they do. (And, I would say, because their greater understanding allows them to better see the gap between what they are doing, and how it should be.)