An Explanation

“”I am wiser than this man, for neither of us appears to know anything great and good; but he fancies he knows something, although he knows nothing; whereas I, as I do not know anything, so I do not fancy I do. In this trifling particular, then, I appear to be wiser than he, because I do not fancy I know what I do not know.

—Plato, Apology (attributed to Socrates)

The Dunning-Kruger effect, named after David Dunning and Justin Kruger of Cornell University, occurs when incompetent people not only perform a task poorly or incompetently, but lack the competence to realize their own incompetence at a task and thus consider themselves much more competent than everyone else. Put more crudely, they're too stupid to realize they're stupid. (The inverse also applies: competent people tend to underestimate their ability compared to others.)

If you have no doubts whatsoever about your brilliance, you could just be that damn good. On the other hand...

The Dunning-Kruger effect is a slightly more specific case of the bias known as illusory superiority, where people tend to overestimate their good points in comparison to others around them. The effect has been shown by experiment in several ways, but in this case Dunning and Kruger tested students on a series of criteria such as humour, grammar, and logic and compared the actual test results with each student's own estimation of their performance.

Those who scored well on these tests were shown, consistently, to underestimate their performance. This is not terribly surprising and can be explained as a form of psychological projection: those who found the tasks easy (and thus scored highly) mistakenly thought that they would also be easy for others. This is similar to "impostor syndrome" — found notably in graduate students and high achieving women — whereby high achievers fail to recognise their talents as they think that others must be equally good.

More interestingly, those who scored lowest on the test, in the bottom quartile, were found to have "grossly overestimated" their scores. Conversely, those with the highest scores underestimated their performance in comparison to others. And what about the underachievers who overestimated their performance? In the words of Dunning and Kruger:

This overestimation occurs, in part, because people who are unskilled in these domains suffer a dual burden: Not only do these people reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the metacognitive ability to realize it.