Those Who Can't Do, Teach

Some people say that those who can't do, teach.  I respectfully disagree.  I say that those who can't do, critique.  Sometimes, the two categories of teaching and critiquing overlap (after all, a large part of the job of a teacher is to critique).  I suspect the confusion over this slight distinction is how the more popular saying originated.  However, in my experience there are far more critics in the world who "can't do" and therefore critique, than there are teachers who "can't do" and therefore teach.