You intuitively know a bad teacher from a good one. When I learned programming both my teachers left me confused. But I rapidly understood that the first was

You intuitively know a bad teacher from a good one. When I learned programming both my teachers left me confused. But I rapidly understood that the first was hard to understand because he was a sort of genius and you had to get to speed if you wanted to follow him, the other was just an incompetent lazy bastard that was there just for the pay (I remember asking him once a simple question on his domain specialty, he just resorted to Google and didn't even find the answer !).