Only teach what the pupil is capable of learning. Better yet, limit your instruction to the information you can actually communicate with your students.
Several potential defenses
In this instance, the fresh information appears to be "in-between" (master vs learner). It isn't entirely the Master's extensive knowledge because he limits his options to suit the novice, nor is it the beginner's actual capabilities because he only improves his dancing as a result of the Master's assistance. As a result, both of them have enacted some knowledge "in between." So what exactly is this knowledge that falls short of what the teacher is aware of and goes beyond what the novice is already aware of?
4. Etc.
Comment: The term expert is used extremely broadly in this context; it simply denotes that the teacher is more knowledgeable than the learner. For instance, teaching arithmetic at the elementary level doesn't require one to be an excellent mathematician. To teach math, you would need to be an expert at least at the university level.