...with my over 20 years of teaching I can honestly say it's
both.
There are times when it takes a good teacher to instruct in a way that best utilizes the learning style of the student. The more experience a teacher has on the subject matter helps tremendously (Boras vs McVay). On the other hand, if the student doesn't make the effort or lacks the cognitive ability to learn the material, even the best teachers/lessons can become less effective than needed.
