I used to believe that local anesthetics were just some homemade brew that the particular dentist/surgeon used rather than an anesthetic restricted to a specific region. I just figured it out during my first year of medical school.
A childhood belief about chemistry

others believed things like this
- Well into adulthood I thought that a local anesthetic meant one from the area near the hospital..— D'sparil
- I used to believe they were called dentist disappointments rather than dentist appointments.— Emma
- I used to think that blood flowed down one leg and up the other.
And I'm applying to medical school....— Nat - I used to think the Black Country region in the UK was called that because everyone lived in darkness there.— K
- When I was in elementary school I use to think that teacher lived at school at their desks all year long.Anon
- For some reason until I was about 10 I used to believe that the dentist pierced your ears.— Kendall.XxX