Jeff Hester of Astronomy magazine wrote:
The other day I got an email from someone claiming to have solved all the outstanding problems in physics and cosmology. Having read a few popular science books, the author insisted that only his brilliant and original perspective could save science from itself. His new “theory” would revolutionize the world!
Welcome to the Dunning-Kruger effect, named after two Cornell psychologists who gave a large group of people tests and then asked them how they thought they did. Kruger and Dunning were startled by what they found. Almost everyone who took the tests was sure that they did much better than average. That was even true for the very worst performers, who wildly overestimated their scores. At the same time, the very best performers typically underestimated how they did.
What Kruger and Dunning found was that if people don't have the skills needed to do well on a test, they don't know enough to assess their own performance. People who know very little can truly believe themselves to be experts because they can't tell the difference. Meanwhile, experts who fully understand just how difficult and subtle things can be think themselves less competent than they truly are.