In the field of psychology, the Dunning–Kruger effect is a cognitive bias wherein persons of low ability suffer from illusory superiority, mistakenly assessing their cognitive ability as greater than it is. The cognitive bias of illusory superiority derives from the metacognitive inability of low-ability persons to recognize their own ineptitude. Without the self-awareness of metacognition, low-ability people cannot objectively evaluate their actual competence or incompetence.

As described by David Dunning and Justin Kruger, the cognitive bias of illusory superiority results from an internal illusion in people of low ability and from an external misperception in people of high ability; that is, "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." Hence, the corollary to the Dunning–Kruger effect indicates that persons of high ability tend to underestimate their relative competence, and erroneously presume that tasks that are easy for them to perform also are easy for other people to perform.

When someone is bad/stupid/ignorant in a field, and thinks they are great/good/guru/expert. This normally happens due to people not having enough knowledge in that field to even know that they are bad at this field. A great place to find and report these people is at /r/iamverysmart

In common usage, it means "clueless of being ignorant" but it's used to add an air of fake scientific authority to a cheap shot. It generally outs the author as an incompetent writer, ironically exhibiting the Dunning-Kruger effect themselves.

Just go on Reddit for a minute and you'll see it in action.

Person who knows very little: Think he knows alot because he has no idea how deep the wormhole goes.
Person who knows a lot: Think he knows nothing because he knows how much he does not know on the subject.

When someone is aware of the Dunning-Kruger Effect as a concept, and incorrectly presumes this awareness of the concept means he is not subject to it.

Donald John Trump (born June 14, 1946) is an American politician, media personality, and businessman who served as the 45th president of the United States from 2017 to 2021.