Try doing something backwards or different than usual. For instance, as a typical right-handed guitarist, try flipping the guitar around and learning to play it left-handed and upside-down. One can get a sense of the experience of beginners.
This is distinct from just learning an entirely new skill. When a teacher learns a new skill, they have no way to evaluate it and are truly just a beginning student. Of course, it is important for teachers to learn new things and that helps their teaching; but it isn't the same as playing upside-down.
When learning a new skill, it is hard to judge what to expect and whether it is being taught well; it is hard to judge the value, and hard to know what it will feel like when mastered. When reversing a guitar (or whatever is comparable for any other skill), all of those things are clear. Thus, the teacher may evaluate and understand the challenges in a way that no other experience can elucidate.