The Dunning-Kruger effect, a type of illusory superiority, is the tendency for incompetent people to self-assess their incompetency too highly. Their lack of knowledge and understanding on a topic robs them of the ability to recognize how much they don’t understand. This often leads low-ability individuals to be overconfident in their own abilities. Conversely, experts often underrate their abilities, as they understand their abilities more exactly, and recognize their shortcomings (this is also known as the impostor syndrome). In short, Dunning-Kruger effect occurs when incompetent and unknowledgeable people not only perform a task poorly but lack sufficient competence to realize that they are incompetent.
In a study by Dunning and Kruger, students were asked to self-assess their skills in a variety of categories, such as logical reasoning. Students were then asked to estimate how they compared to the rest of their class. Students with high self-assessments underestimated their ranking, while students with low self-assessments overestimated their ranking.