Everyone rises to their level of incompetence.
... put another way ...
Everyone rises to at least one level above that at which they are competent.
One of the criteria of choosing people in key positions is that they have to be quite foolish, at the limit of being able to do their work. The reason: such a man will never argue with his boss, and will do any foolish thing required from him in order to save his position. In fact, he won’t even be able to judge what he is doing - he'll just do what he is told to do.
The Peter Principle was first introduced by L. Peter in a humoristic book (of the same title) describing the pitfalls of the bureaucratic organization. The original principle states that in a hierarchically structured administration, people tend to be promoted up to their "level of incompetence".
The principle is based on the observation that in such an organization new employees typically start in the lower ranks, but when they prove to be competent in the task to which they are assigned, they get promoted to a higher rank. This process of climbing executive ladder can go on indefinitely, until the employee reaches a position where he or she is no longer competent. At that moment the process typically stops. Established rules of bureaucracies make it very difficult to "demote" someone to a lower rank, even if that person would be much better fitted and happier in that lower position.
The net result is that most of the higher levels of a bureaucracy will be filled by incompetent people, who got there because they were quite good at doing a different (and usually, but not always, easier) task than the one they are expected to do.
(funny movie)
