In 1999, social psychologists David Dunning and Justin Kruger did a series of studies evaluating people’s competence in certain areas, including grammar, humor and logic. The people in the studies were also asked to evaluate their own abilities in each area. Dunning and Kruger found that people who scored very low on the tests tended to overestimate their abilities. Later research has indicated that a similar principle applies to other areas as well. People who lack skills also tend to lack the ability to realize their shortcomings. In other words, those who don’t know much think they know more than they actually do.

  This principle has become known as the Dunning-Kruger effect after the researchers who discovered it. The Dunning-Kruger effect occurs because only when people have skills in a given area are they equipped to evaluate their own skills. For example, in some situations it takes a scientist to recognize bad science.

  Moreover, most people are biased in their own favor. They want to believe that they are more capable, knowledgeable and maybe even superior to others. And when someone really wants something to be true, it can be hard for them to admit that it isn’t.