The Dunning-Kruger Effect named after David Dunning and Justin Kruger of Cornell University, occurs where people fail to adequately assess their level of competence — or specifically, their incompetence — at a task and thus consider themselves much more competent than everyone else.
This lack of awareness is attributed to their lower level of competence robbing them of the ability to critically analyze their performance, leading to a significant overestimation of themselves. In simple words it’s “people who are too stupid to know how stupid they are”.
The inverse also applies: competent people tend to underestimate their ability compared to others; this is known as impostor syndrome. The principle is illustrated indirectly by the common saying that “I’ve learned enough about ________ to know what I don’t know.” The implication is that someone who hasn’t learned much about the subject would have no appreciation for how much there is to learn about it, and so might grossly overestimate their level of understanding.
If you have no doubts whatsoever about your competence, you could just be that damn good. On the other hand…