The Dunning-Kruger effect describes a disturbing cognitive bias that afflicts us all. People with limited expertise in an area tend to overestimate how much they know—and we all have gaps in our expertise. That disconnect may explain why some patients turn to "Dr. Google" to make at-home diagnoses of complex medical problems, as well as the missteps we all make from time to time, from fixing the plumbing to representing ourselves in a court of law. Over the years, the Dunning-Kruger effect has gone from a scientific hypothesis to a popular meme, pulled out in shouting matches across social media. In the hierarchy of insults, there are few more powerful than invoking the idea that your opponents are so stupid that they don't even know how stupid they are. It's just one step short of calling the other side a bunch of Nazis, aka Godwin's Law—the traditional way that flame wars end.

David Dunning, now a social psychologist at the University of Michigan, and Justin Kruger, now at NYU, proposed their namesake effect in a famous 1999 paper. In a series of surveys combined with tests, they found that students from Cornell who scored in the bottom quartile estimated that they had scored in the third quartile, and identified related forms of unearned confidence. Since then, Dunning has extended his investigations into the mechanisms of trust and belief. OpenMind co-editor Corey S. Powell spoke with Dunning about his ubiquitous effect and how it colors self-knowledge for us all. (This conversation has been edited for length and clarity.)

Read the complete article in Scientific American