As black is the opposite of white, I used to believe that blue was the opposite of red. Also, bannanas were the opposite of apples, and giraffes the opposite of elephants. It's not such a bad analogy, when you think about it.
A childhood belief about physics

others believed things like this
- I used to believe that the opposite of “impressed” is “pressed.”Anon
- I used to believe that if I could kiss my elbow that I would turn into a girl (the opposite sex).— Rusty
- i used to believe that everyone was born as the opposite sex, and that you changed when you started school.— llama
- I thought that old movies were black and white because the world was black and white then. — K
- I used to think that the old days were actually black and white because of the old black and white pictures.— Leigh Taylor
- i used to associate the word appetite with apples, if you ate apples, you had an appetite. — elly