I used to think that before rescuing a drowning person a lifeguard (or anyone really) had to put their PJs on. This was because when I had swimming lessons I had to 'rescue' a brick from the bottom of the pool while wearing my PJs. When I was 13 I finally discovered this wasn't true.
A childhood belief about swimming pools

others believed things like this
- I used to think that a "pool shark" was an actual shark that lived in a swimming poolAnon
- I believed that the ladder on the back of a trailer/rv led up to a swimming pool.— marilese
- I used to believe that if you farted while swimming in the pool, it could propel you foward really fast.— Rick
- Up until I was in 3rd grade I believed my bathing cap is what kept me afloat in the swimming pool! Anon
- When I was a kid I used to think the "carpool lane" was an actual pool cars went swimming in— skeez
- I believed that the Kreepy Crawlie used to clean our pool, would follow me around the pool and eat me. — Mother-of-2