The Peter principle states that "every employee tends to rise to his level of incompetence". If someone is good at her job, she'll be promoted into a job that demands different skills. If she's good at the new job too, she'll be promoted again, requiring yet another set of skills. One day, she will arrive at a job for which she is wholly unsuited, and there she will stick. Since when did a manager ever get sacked for anything?
http://timharford.com/2018/08/the-peter-principle-is-a-joke-taken-seriously-is-it-true/