I used to believe that the Sailor Soldiers from Sailor Moon were actual sailors, navigating the galaxy in giant ships.
A childhood belief about cartoons

others believed things like this
- When I was young, I used to think I was Sailor Moon— Emma
- I used to think that if you ate spinach that eventually, you would be as big as popeye the sailor man.— Corrine
- I was convinced that Gorilla soldiers in Vietnam in the 70's were real Gorillas attacking other Soldiers.— Mario
- When I was a little girl, I used to believe that the moon was actually a giant, glowing white
Anon - I used to dig a super deep hole thinking it
would transport me to the galaxy — Rafaella - I thought "The Hitchhiker's Guide to the Galaxy" was a somewhat casual manual for astronauts.— Katya