Many times people get promoted for the wrong reasons:
When deciding who to promote to a position of authority, the performance of the person in a front line role is important, but we need to look much more at the holistic aspects of the person in the role such as:
These are the criteria that truly matter when choosing who to promote into a leadership role.
By the above test the great nurse may or may not be a great leader of other nurses (she has 1 of the 4 requirements) and the bumbling teacher should never be promoted to principal (he is missing 1 of the 4).
Just having number 4 is only a small part of getting the promotion. In great organizations like yours and mine, everyone has basic competence for the work they are doing, so it really comes down to the other 3 factors.
How do we decide about the other 3 factors? Leaders take everything they know about each of the candidates based on what they have observed and they make a judgment as to who will make the best leader. We toss aside everything: seniority, sex, race, who wants it the most, who everyone thinks deserves it, and we pick the person best suited for the job.