I was pretty clear on what happened during sex - the penis went into the vagina. But I had no clue about erections. I thought that the penis just went straight down, and that in order to have sex, a man and woman would need to lie head-to-feet, with one of them faced to the side, fit together sort of like jiwsaw pieces.
I concluded that it was a very complicated process, that required lots of practice, forethought, and a good grasp of geometry. I'm not sure how I rationalized the idea that people had sex facing each other. I just thought that was another myth about sex.
A childhood belief about sex

others believed things like this
- i thought getting circumcised was to get the head of the penis cut off— Dee
- i used to believe that a penis was the same as a vagina except really long— *stupid*
- i used to believe that if you have sex for too long, the penis would stay in your vagina— Angela
- i used to think that having sex was licking the persons vagina or penis until u got tiredAnon
- I used to think that Frankie Avalon sang, "Hey Penis, Oh, penis..." instead of "Hey Venus."Anon
- I used to believe that gay sex involved a man sticking his penis inside another man's penis.Anon