I used to believe that room numbers in hotels were literal. So, if I was staying in room 305, it meant there were more than 305 rooms. I then found out that it just meant the 5th room on the 3rd floor.
A childhood belief about excursions

others believed things like this
- I used to believe Jesus cleaned my room.— Angelina
- I used to believe that when we left a room the TV set started to speak about other things — Nur
- I used to think that the upper struture on the caboose was the rest room.Anon
- I used to believe the living room furniture would party after we all went to sleep.— Ellen
- I used to turn the TV off when I left the room so I didn't miss anything.— S.Lee
- My older brother used to tell me that if I "untied" it, I'd fly around the room like a balloon. — Gullible youth