Some of these people are simply ego maniacs who live in a fantasy world of sorts where they are in some way superior to everyone else. We talk often about leaving the excess ego at the door when you come to work in the morning. It is difficult for these people to do that. Keep in mind that most ego maniacs are typically covering up for some form of insecurity. There's no question that the human ego is at the root of a number of problems in businesses everywhere.
Egos range from almost none to out of control.
A little ego is good since it helps with confidence levels. But to allow an ego to run out of control to the point where problems occur only because of someone else or the only right answer is your answer is a prescription for major trouble. People with runaway egos often are in denial about their behavior. They see themselves as tremendous employees or managers with few, if any, faults. The result of this type of attitude is resentment from fellow employees.