A bit meta: That people who were wrong or mistaken about something just needed it explaining more clearly, and then they would stop saying things which are wrong or mistaken.
I wasted far too many years of my life trying to convince father-in-law of so many things, only to realize there is nothing that can be said to disabuse him.
The problem wasn't the lack of facts or clarity of explanation, it's that he is fundamentally incapable of acquiring new information if it's inconsistent with his prior understanding or belief.
Moreover I realized that where I am ashamed of being inaccurate or uneducated about something (and so am keen to correct myself), for him it's always the case that I must be wrong or mistaken, because he can never be wrong or mistaken.
When I was much younger: that normal people could see much further than me.
One of my oldest memories is going into a McDonald's for the first time with glasses; I stopped and read the entire menu, because I couldn't believe normal people could read it as soon as you walked in. I always had to get up to the counter to make it out.
I think Blackadder aged pretty well.