The Dunning Kruger effect is a cognitive bias in which individuals, who are unskilled at a particular task, believe themselves to possess above-average ability in performing the task. On the other hand, as individuals become more skilled in a particular task, they may mistakenly believe that they possess below-average ability in performing those tasks because they may assume that all others possess equal or greater ability. In other words, “the miscalibration of the incompetent stems from an error about the self, whereas the miscalibration of the highly competent stems from an error about others” (1).

The first identification of this type of cognitive bias is unknown, but the idea has been known and expressed for a long time. Shakespeare, in “As You Like It,” states “the fool doth think he is wise, but the wise man knows himself to be a fool” (2).

The Dunning Kruger effect was formally given its name in 1999 when researchers noted that, for a given skill, incompetent people:

1) Overestimate their personal skill level.
2) Fail to recognize genuine skill in others.
3) Fail to recognize the extent of their incompetence.
4) Are able to acknowledge their own lack of skill, if exposed to training in the skill tested (3) .

Source:

(1) Kruger, Justin; David Dunning (1999). “Unskilled and Unaware of It: How Difficulties in Recognizing One’s Own Incompetence Lead to Inflated Self-Assessments“. Journal of Personality and Social Psychology 77 (6): 1121–34

(2) Fuller, Geraint (2011). “Ignorant of ignorance?”. Practical Neurology 11 (6): 365.

(3) Kruger, Justin; David Dunning (1999). “Unskilled and Unaware of It: How Difficulties in Recognizing One’s Own Incompetence Lead to Inflated Self-Assessments“. Journal of Personality and Social Psychology 77 (6): 1121–34