Rented a plane and instructor on Vancouver Island once.
(1) Aiming at a sloping horizon for the first time in my life I was having trouble flying straight and level. I thought that this was entirely down to me not being used to a non-flat horizon. But after a while the instructor said "yes, this one has never been quite the same since the accident".
(2) Him: "let's go and look at that waterfall." We fly straight towards a cliff. "OK, that's close enough isn't it," I say. "Nah, we can go a lot closer than that." Repeat, several times, for quite a while. Eventually he says "OK, you can turn now, I won't insist on you going any nearer if you're not comfortable with it".