That most people are much dumber than they initially appear to be. “Average intelligence” isn’t enough to form a basic understanding of the world.
One time I tried pump my fuel and it kept stopping right away. I moved pumps and the same thing. I was looking down the hole to see if anything was blocking it, I went inside to inform the attendant their pumps might be malfunctioning. Then I realized, the night prior I had already filled up. I’m a dumbass.
To my credit, however; it is my routine to fill up every morning (I drive courier) A night fill up was off routine. Still a dumbass.