When I was first learning subtraction with two-digit numbers, we were told that to subtract a big digit from a little digit, you have to "borrow a one" from the tens place, which of course reduced the digit in the tens place by one. All true.
The problem was that I had been told very clearly as a child that when you GIVE something you get to keep it, but when you BORROW something, you have to give it back -- it isn't really yours. When the teacher completed the problem on the blackboard, I asked her when we were going to give the one back. She looked at me as if I was crazy, and said that you don't give it back.
I found this rather disturbing, and from that day to this I have always thought that subtraction was mean and unfair.
A childhood belief about counting

others believed things like this
- I thought Maria Carey's 1998 ballad was 'I'd give my arms' instead of 'I'd give my all'.— Briony Maggs
- I used to believe that a bank was a place where they give out money to peopleAnon
- I used to believe that the lyrics to Bon Jovi's "You Give Love a Bad Name" were "You give love a Band-Aid".Anon
- When i was child i used to believe that when i lose one tooth, a little mouse will give me some money.— Daniele
- I used to think eating raw potatoes would give you "BEZORES".
Our family doctor told me this— Moodycop - i used to beleive that if you chewed gum it woul give you warts in your mouth my sister told me this— sunney jim of the pearl