When I was on holiday with my parents once, we saw a flooded quarry. I asked why nobody was swimming in it and my mother told me it was too deep to swim in. For years I believed that there was some depth at which water became too deep to swim in and you would simply sink to the bottom. Even now I'm wary of swimming in deep lakes!
A childhood belief about water

others believed things like this
- I believed they put heated coils in lakes for the ducks to swim in the wintertime.Anon
- If you eat 30 minutes before swimming, you will sink.Anon
- I used to believe that, in cities, if you dug deep enough in anyone's lawn, eventually you'd hit the concrete.— Kevin Fox
- When I was a kid I though facial hair on a man is what gave them the deep voice — Adrian Z.
- i used to believe there were invisible sharks in the deep end of the pool, thanks to my older brother.— Melissa
- I used to dig a super deep hole thinking it
would transport me to the galaxy — Rafaella