I went to church every Sunday my whole life because my dad was a preacher but still it did not occur to me until I was in 5th grade that there was no hymn called "Standing on the Last" - that was just what our music leader would say when he introduced each hymn so everyone would rise on the last verse.
A childhood belief about hymns

others believed things like this
- I used to believe God had a pet tortoise. There was a hymn we sang that went "Great things he hath taught us"— Lozza
- When he was a kid, my husband thought the hymn "bringing in the sheaves" was "bringing in the cheese."Anon
- I used to think that church songs were pop music. Well, we did sing them in church every week...— Roxy
- I used to believe that the sun shone brighter on a Sunday! Sunday in all languages is named after the Sun!!!— Vasu Moses
- I used to believe that since guys peed while standing up, then they must poo while standing up too.— Stupid girl
- My music teacher once said that music in an electrical piano was made by little tiny men that lived inside it.Anon