I’m guessing you’ve had this experience: a co-worker or associate of some kind does things very badly. S/he does them badly all the time. Your perception—and you probably don’t think about this at all—is that he (let’s call him Buddy) simply does not know that he’s performing badly. If Buddy knew, for example, that his reports were full of errors, he’d fix them. It turns out you’re right, right about all the Buddies. The same thing that causes Buddy to make all the errors also makes him not bright enough to realize that’s what he’s doing.