Here is a stupid thing I believed when I was a child:
I did not understand that not all seals are airtight. I never said anything to my parents, but I would get scared sometimes when we would drive someplace and neither the AC nor the heat was blowing, because I thought that was how the air was getting in the van.
I thought that if we had it turned off for too long, and didn’t open a window or something, that we might breathe up all the air and die before we got where we were going. So I would always pester my parents to turn the air back on if I thought it had been off for a long time (which, for a child in a car, is maybe 10 minutes), because if I didn’t, I would be reduced to not talking and trying to take very small breaths or hold my breath until we got there.
Probably for the best that I never aspired to be an astronaut.