What I'd throw in there as well is competence noise. The people who are sitting with someone day-to-day can tell whether they are competent. But the person who decides who gets promoted is somehow blind to this.
Sometimes yes, but I also observed that sometimes it was necessary to do, since no other suitable person showed up.
Also, I would add that what surprises me how slowly many people can improve.
Incompetent manager: "Hey uh can you pop open that firewall for me?"
Me: "That's against corporate policy. You'd need to follow procedure xyz."
Incompetent manager: "My good friend, J could open that firewall in 15 mins flat. J opened the firewall for me 4 times last week. He could show you how if you don't know what you are doing, its no problem."
Me: Facepalming "Didn't you hear what I just said?"
Of course the above happens in a meeting with a congregation of people.