Dr. David Dunning of Cornell University and Dr. Justin Kruger of the University of Illinois report in the Journal of Personality and Social Psychology experiments that show incompetent people don't know how badly they perform. Incompetent people perform both badly and don't know they perform badly, which hinders chances for improvement.
In logic tests, those with performance in the lowest eighth thought they performed in the top third. Those in the lowest tenth on grammar also thought they performed in the top third. Those who really were in the top third underestimated their performance.
Competent people accurately revised opinions of their performance when shown how their results compared to others. Lower performing incompetent people, however, did not lower estimates of their own performance when shown the performance of others, with some even further inflating their own performance.
This explains people who insist they are doing well when their poor work is pointed out. It also explains why they keep doing things wrong. The good news is that the researchers also reported the performance of incompetent people improved when they were given some training in logic and other tested tasks.
Incompetent performance may not be an inability to learn, but an inability to recognize errors that are part of the feedback information process by which we learn how to perform well. People who are reasonably self-critical probably have a learning advantage.