I used to think that the reason that we are able to see is that light somehow comes out of our eyes and illuminates the scene in front of us. I apparently never thought about why this doesn't work in dark rooms!
However, I have since read that grown adults used to believe the same thing in the Middle Ages, so it must be a common misconception.
A childhood belief about eyes

others believed things like this
- if you read the bible in the dark your eyes would pop out— chriistabelle
- I was born brunette with brown eyes and dark hair, i thought people with blue eyes, had water in them.Anon
- i thought grown ups read in a different language!Anon
- I used to believe if you read a book in the dark, you would go blind.— Ellen
- I used to believe that grown-ups, mothers in particular really did have eyes in the backs of their heads.Anon
- I don't know why, but for some reason I thought that blinking your eyes powered your speech.Anon