I used to think "lobotomy" meant a brain transplant, and that brain transplants existed. In other words I thought that people getting lobotomies were getting the brains of other people put into them .. organ donors presumably. I learned the truth when one day during a conversation about consciousness I started to say "if you get a lobotomy ..." and then I stopped myself realizing I was about to say something really stupid. I said "wait never mind" and let someone else talk for a minute.
A childhood belief about technology

others believed things like this
- I used to believe that people who wear glasses did had a second brain!— Onessa
- My brother used to tell me if I picked my nose I would become more stupid because bogey were brain cellsAnon
- I used to believe that people's brains differed in colours. I always wanted purple brains for some reason.— Katrina
- I thought that big people are necessarily smarter because there brains would be bigger— Quatsch
- I didn't mind eating lambs brains when I was a kid because I thought it would make me smart.Anon
- I thought my brain would explode if it was in the sun too long— Heather