Just read an article by Justin Kruger and David Dunning (1999) from Cornell University about the way that people who know less about a particular area overestimate their own skills and knowldge. Interesting also that further training helped people to perceive their limitations.

As Kruger and Dunning note in their abstract: “Across 4 studies, the authors found that participants scoring in the bottom quartile on tests of humor, grammar, and logic grossly overestimated their test performance and ability. Although their test scores put them in the 12th percentile, they estimated themselves to be in the 62nd. Several analyses linked this miscalibration to deficits in metacognitive skill, or the capacity to distinguish accuracy from error. Paradoxically, improving the skills of participants, and thus increasing their metacognitive competence, helped them recognize the limitations of their abilities.”
Full text here

From Aide-mémoire