I used to believe that the sign language used by Deaf people involved fingerspelling every word. Probably due to reading a Happy Hollister book with a Deaf character who taught the Hollister kids the finger alphabet to use for silent communication purposes in their "detective" work.
A childhood belief about speaking

others believed things like this
- When I was little ,I used to believe that deaf people didn't have ears.— rainbow
- I'm deaf in one ear. Until I was 7 I believed that if I didn't sleep on my good ear, dinosaurs would eat me.Anon
- I used to beleive when ppl didn't talk (deaf ppl) they lost their voice and could never talk again!— Tiara 10
- I used to believe, that I am able to speak every foreign language only by learning "their" alphabet.— matej
- When I was learning the alphabet,I thought elemeno was one word.— Rick H.
- I believed that the word optimistic was something to do with opticians and being happy with your eyesight.Anon