Someone I know thought that your favorite number has to be the same as your age, so on your birthday your favorite number is different.
A childhood belief about birthdays

others believed things like this
- when i was little i believed that your social security number was the number you were born on the earth — christine
- When my favorite Uncle died, I thought if I stared at him in his coffin he would open his eyes and be alive.— Cindy
- When I was little I thought you could get arrested if you accidentally skipped a number while counting.— Hailey
- My favorite excuse:
Must be those trouser geese again!— Tootie Fruity - I thought everyone only had a set number of breaths before they died.
I breathed slowly for a long time.Anon - My brother believed that bacon(his favorite food) was from horses. — Jenn