Re: The obverse also applies in some cases
When I was at school, in the mid 60's, we had a Maths teacher who was trying to teach us Statistics. He would write on the board a long and complicated formula, followed by another line which was only slightly different from the first, then another, then another, finishing off near the bottom of the board with "Therefor", and the expression that he was supposed to be proving. When any of us put their hands up and asked how he had made that ginormous leap, he would reply "But it's obvious, isn't it?" Not to us it wasn't. We never learned anything from him, and we called the course "Applied Guesswork". I don't think anyone in my year passed that course.
Biting the hand that feeds IT
