I used to believe that "caller i.d." was actually "caller idea" becuase you would have an IDEA about who was calling you.
A childhood belief about telephones

others believed things like this
- Up until 5 seconds ago, I had no idea wat a gherkin was— It's a little cucumber, stupid!
- I used to think Hungary and Turkey were the same country... I have no idea where that came from...— Skylla
- When I was eight, I thought my dad could translate what the birds were saying. I have no idea why.Anon
- Good looked exactly like George Washington.
I have no idea where I got this.— Leen - I used to believe that slugs were deadly and they would bite you and kill you. 0_o Where did I get that idea?— What was I thinking?
- I used to think being engaged meant being in jail. I have no idea how I came to that conclusion.— CNB