Someone teaches you something as a kid, you take it at face value, you carry on believing it without ever really thinking about it, you say it when you're an adult, everyone laughs at you.
What are yours?
My mum said something to me when I was about 8 that I misinterpeted as her saying Greenpeace were in possession of a nuclear bomb, and used it to pressure governments into protecting the environment.
Somehow I never discovered or worked out this was obviously not true and when I was 19, I confidently brought it up in a debate with someone who was a Greenpeace supporter. Their facial expression was amazing.
Tell me yours!