Dunning-Kruger Effect
People with limited ability at a task tend to greatly overestimate their competence, while highly skilled people often underestimate theirs. The less you know, the more confident you feel about knowing it.
Origin
Named for psychologists Justin Kruger and David Dunning, who published "Unskilled and Unaware of It" in 1999. Their studies found that bottom-quartile performers estimated themselves near the 62nd percentile. Recent criticism, notably a 2020 analysis, argues the effect is largely a statistical artifact of regression to the mean — a debate that remains unresolved.
Everyday Use
This concept is typically invoked as a depressing feature about workplace colleagues — but a more charitable perspective would tell us that it's a reminder that it's very hard to know what to be good at, how we are doing on those fronts, and how others fare in comparison, all things being equal.