I just ran across this quote and thought to share it.

“What you need to remember, with these guys, is that they don't know they're con men. They're wildly overconfident.  Omnipotence, omniscience--that's part of the mythology... Your guy can walk in the door and promise something he personally doesn't know how to do, and not even realize he's bullshitting about his own capabilities.  It's a special kind of gullibility."

William Gibson, Novelist/Essayist

... sounds like the description of a sociopath.