A childhood belief about getting pregnant

When I was in 9th grade, some friends and I were talking about a girl at our school who had gotten pregnant. One of my friends (a very naive 15-year-old boy) said, "I can't believe she wanted a baby so young!" Another friend answered that she doubted the girl actually WANTED to get pregnant, and that it was most likely an accident. My friend (the boy) said, "How do you accidentally get pregnant? Why didn't she just not have sex for a few weeks after she found out she was pregnant?" We were all completely puzzled. Then we made him explain what he meant:

My friend was under the impression that the reason it took 9 months to have a baby was that you had to have sex EVERY DAY for 9 months to make the baby. Like each time would add a piece. And if you just stopped doing it, the pregnancy would "go away".

The rest of us could not stop laughing. We collectively explained the truth to him, though he did continue to be mystified by the female reproductive system for at least a few years after that.