In response to the idea that beginners should not be taught in ways that need to be unlearned later on if they take it to higher levels: I agree. However, I also believe the greatest impediment for most people to learning anything is internal. But that’s not to say it’s some psych out thing that can be overcome w a better attitude. Internal problems are entirely real and need respect. Confusion and frustration are central to the learning experience and a good teacher makes it central to teaching as well. Richard Feynman is a great teacher and his books do not teach stuff you need to unlearn even though he teaches simplifications all the time. I cannot say the same about all of my books! Apologies!