Experts, novices, and intermediaries

You don't need to be an expert to teach something.

You merely need to be more adept at what you're teaching, than the person(s) you're teaching.

Or more precisely, more adept at communicating and explaining the subject matter, nuances, and best practices of what you're teaching than your colleagues.

A musician who knows his instrument--the notes and the scales and a few jingles--is more than able to teach a novice the same thing. And, if he can find a way to communicate that knowledge better than an expert can, he can charge just the same and stay competitive. Because his clients aren't paying for his expertise, their paying for his skill of transmitting knowledge and know-how.

He's no expert, and he doesn't need to be. He just needs to be the best teacher he can for the people who pay him to teach.