The Peter Principle
The Peter Principle (book ) states that “every employee tends to rise to his level of incompetence.”
Someone who is good at their job is likely to get promoted. However, the promoted position will likely require different skills. If they’re good, they may get promoted again, but if not, they will stay. At some point, each employee in an organisation will be incompetent at their position.
I like this short take on the Peter Principle by Tim Harford .
The Peter Principle is a specific case, the case of people, of the Generalised Peter Principle which states that "Anything that works will be used in progressively more challenging situations until it fails." See rule number 1 of indoor games.
The Peter Principle was an observation originally meant as satire. Laurence Peter later wrote a book called The Peter Principle: Why things always go wrong .