It's a question we all hear all too frequently. The simple amazement that someone that professes to have great talent or knowledge in a certain area (or, for some, in everything) is sensationally wrong so often.
In a nutshell, these two researchers discovered a direct and inverse correlation between a person's belief in their superiority and their actual dominance. From the study: "Not only do these people reach erroneous conclusions and make unfortunate choices, but their incompetence robs them of the metacognitive ability to realize it.”
At the same time, the more adept someone is, the less confident they are of their own competence.
So, the next time someone proclaims that they are absolutely, 100% right, you know you have science on your side when you shrug, sigh...and walk away.