Dunning-Kruger Syndrome is the phenomenon whereby people who have little knowledge systematically think that they know more than others who have much more knowledge. In a phrase, clueless people think they are smart.
Though many people have noticed this, it was rigorously demonstrated in a series of experiments performed by Justin Kruger and David Dunning, then both of Cornell University. Their results were published in the Journal of Personality and Social Psychology in December, 1999.
Their study involved giving people tests of their knowledge in various domains, then asking them how they thought they did. People at the bottom of the results tended to hugely overestimate their abilities. As Dunning and Kruger noted,
"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." Meanwhile, people with true knowledge tended to underestimate their competence.
This phenomenon manifests itself in all walks of life, and is surely familiar to users of Usenet and IRC discussion groups.