This phenomenon is something you have likely experienced in real life, perhaps around the dinner table at a holiday family gathering. Throughout the course of the meal, a member of your extended family begins spouting off on a topic at length, boldly proclaiming that he is correct and that everyone else’s opinion is stupid, uninformed, and just plain wrong. It may be plainly evident to everyone in the room that this person has no idea what he is talking about, yet he prattles on, blithely oblivious to his own ignorance.
The effect is named after researchers David Dunning and Justin Kruger, the two social psychologists who first described it. In their original study on this psychological phenomenon, they performed a series of four investigations and found that people who scored in the lowest percentiles on tests of grammar, humor, and logic also tended to dramatically overestimate how well they had performed. Their actual test scores placed them in the 12th percentile, yet they estimated that their performance placed them in the 62nd percentile.