David Dunning and Justin Kruger, psychologists at Cornell and the University of Illinois, wanted to dig further into the known fact that taken as a whole across large populations, the average person rates himself as above average in skills and knowledge. Plainly, the average person cannot be above average in his or her skills, so how is it that we do not know ourselves? Ignorance breeds overconfidence, they say; particularly in fields which people know just enough to be dangerous. When Dunning and Kruger surveyed and tested Cornell undergraduates on such skills as logical reasoning and humor, the same pattern was repeated every time. Those with the worst test scores grossly overrated their performance and skills compared to others. The two psychologists quote Charles Darwin on this phenomenon: "Ignorance more frequently begats confidence than does knowledge".

The two have a few theories about how this could be: maybe incompetent people have trouble observing the world around them, or maybe the world does not provide good feedback. "It's possible that as humans we desire to be ignorant of our abilities", Kruger says.