What about managers who are clueless about their people?
Someone goes to the boss every day, telling him what a hot shot he is. In the meantime, the real work is done by someone who never brown-noses, never shirks a responsibility, never runs away from work, does the heavy lifting, is always dependable, and typically gets a kick in the can from upper management, along with a lot more work, as a reward.
One of the problems of the workplace is that managers really don't know their people, have no idea what they do all day, and cannot appreciate the myriad of problems that are solved below their organizational level by people who never complain and never blow their own horns. You would think that a manager would know who their heavy-hitters are. You would think that a manager would appreciate someone whom he can always count on. But not necessarily so.