I used to believe that there were two words; impossible and inpossible. Impossible things could not be done while inpossible things were the opposite. Obviously those things are just possible.
A childhood belief about spelling

others believed things like this
- I used to believe that it was impossible to survive cancer.Anon
- When I was little I used to think that it was impossible to travel to the moon because I saw it very small
— Kautar - I thought it was impossible for anyone to lift more than their own body weight. Just seemed to make sense..— Xenomorph
- I used to believe that you could pass things down the telephone.Anon
- I used to believe that when you lost things, it sometimes was because they had really vanished. — fluffy
- I used to think that when you get older you could go back and redo things. — cobra