As a child, I'd heard of the idea of "wall to wall carpets", and was quite convinced that some houses had carpets going down one wall, along the floor, and up the next wall. When I was in college, one of the lecture halls had exactly this and I realised that part of my brain still had this misconception. Luckily, I managed not to make a fool out of myself on my first day.
A childhood belief about around the house

others believed things like this
- I used to believe that at the end of the universe was a big plywood wall.— matt
- I used to believe that the cool aid man was evil and he'd break through my wall and get me.— tammy
- I use to believe that my grandpa invented the wall because his name was WallyAnon
- I had a little hole in the wall under my bed when I was little and I thought that Fraggles lived in there.....— Tina
- I used to think that Hadrian also built the Great Wall of China.— Spacey
- I used to think that The Great Wall of China was made out of porcelain.— Morten Vestergaard