Too often people who want to acquire a skill seek out teachers because they have expertise in that skill. Seems logical.
The gymnast who brags that her coach was an Olympian. The student who thinks he should only learn German from a native German-speaker.
Two flaws with this approach:
1) some people have a high level of skill despite (not because of) the way they learned
2) the skill of performing and the skill of teaching/motivating/coaching other people are unrelated
The best teachers leave repeated evidence in the form of students who have learned to excel because of them.
Next time you’re looking for a great teacher, forget asking how good she is, ask how good her students are instead.