https://leadershipfreak.wordpress.com/2016/10/23/peter-drucker-the-truly-dangerous-thing/

Wrong questions when promoting from within:

When you need a supervisor for a team of engineers, the question isn’t, “Is this potential supervisor a good engineer?”

Beware the right answer to the wrong question.

“Yes, this person is doing a great job in their role as an engineer. Let’s promote them to supervisor.”