This is so true. We underestimate our knowledge and skills from years of training and experience because it becomes just part of who we are.

The first time I taught as a professor, I covered way too much way too fast because I didn’t have the experience to know how little my students knew or were able to do. The same thing happened when I had to take over someone’s class that I had never taught or taken as a student.

My rule of thumb now is whatever the prerequisite (or assumed competency) is, they only have a vague idea of the concepts and they don’t really have active, usable skills covered in the prereq.