I’m beginning to think that the hardest part about teaching (for me, at least, right now) is figuring out where to start so that the student(s) will understand. What do you assume that the student knows?
You can’t know what that student knows when they walk into the classroom, or signs up for a course. Even if they took another course, how much did they learn?
Does this mean that you should define rigorous prerequisites, and hold students to them?
I prefer that the instructor provide a lot of “catch-up” material for students who don’t understand the assumed fundamentals. Have a few handouts for those who may not have fully grasped everything you need them to know.
Not that hard.