Peter principle

Observation that in an hierarchy people tend to rise to "their level of incompetence." Thus, as people are promoted, they become progressively less-effective because good performance in one job does not guaranty similar performance in another. Named after the Canadian researcher Dr. Laurence J. Peter (1910-90) who popularized this observation in his 1969 book 'The Peter Principle.' 

Knowing the Peter principle and preventing employee stagnation can help to increase profits for your business in the long term.