My friend used to think that a 'gander' meant a group of geese, not a male goose. So, she thought the expression "What's good for the goose is good for the gander" meant "What's good for one is good for all!" Her version made perfect sense...it was just wrong! :)
A childhood belief about speaking

others believed things like this
- I thought that a person's motorskills meant how good they were at driving!Anon
- I thought when someone was described as being "mild-mannered" it meant they didn't have very good manners— Samilton Duerheiser
- I used to believe wolverines made good housepets -- I was wrong.— I told you so
- When I used to see a sign saying "Littering Fine" I thought they meant if you littered REAL GOOD!— Lou V.
- I used to think that if a movie was advertised on the side of a bus, that meant it was really good. — Aretia
- I used to believe that you could catch AIDS from just looking at a nud girl. Good thing I was WRONG— Mbm4615