i used to believe that the expression "know it like the back of my hand" was "know it like the back of my head," until my uncle asked me how well i knew the back of my head. i told him, not very well, and that i never did understand the expression.
A childhood belief about speaking

others believed things like this
- My mom always told me she had eyes in the back of her head. — Ellana
- I really believed, underneath her hair, my mom had an eye in the back of her head.— Jessica
- When I was little, I believed my parents really had eyes in the back of their head.— Tera
- i used to believe that my preschool teacher had eyes in the back of her head.Anon
- My friend told me she had invented the expression 'Gordon Bennett' and I believed her!— SueE
- I used to think that the expression "The former or the latter?" was actually "The farmer or the ladder?" — Fitzwilliam