"Ignorance more frequently begets confidence than does knowledge," wrote Charles Darwin in The Descent of Man (1871). Experimental findings reported in 1999 by social psychologists David Dunning and Justin Kruger bolstered Darwin's insight. They tested people on their knowledge of grammar and logic and found that many of the people who did badly on the tests rated their performance as being well above average. On the other hand, those who did well tended to underestimate how well they had done.
The now eponymous Dunning-Kruger effect is a cognitive bias in which people "wrongly overestimate their knowledge or ability in a specific area. This tends to occur because a lack of self-awareness prevents them from accurately assessing their own skills." In other words, incompetent people are often too incompetent to realize just how incompetent they are. (It should be noted, however, that some now suggest that the Dunning-Kruger effect is not a real phenomenon but arises from how the researchers parsed their data.)
