Exactly. It's very hard to judge how hard it is to understand something when you already understand it. This is also why video games with puzzles need extensive

Exactly. It's very hard to judge how hard it is to understand something when you already understand it. This is also why video games with puzzles need extensive play testing. Because the puzzle designer, already understanding how to solve the puzzle, is terrible at judging how hard it is to understand the puzzle. It seems that our counterfactual reasoning ability largely breaks down when it comes to understanding. For some reason we can't evaluate the question "what would I think if I didn't already understand this?" > Notes written by professors who teach smart kids, optimize for minimizing confusion, and do real user testing are often much better than the best books, in my experience. Yeah. Though smart kids get confused less easily, which means lecture notes written to teach dumb kids are even less confusing.