i used to believe that your reflection was you from another dimension and everytime you move away, the person in the mirror dies.
A childhood belief about mirrors

others believed things like this
- i always thought I was the reflection and your reflection was a personAnon
- I used to believe that when you cracked a mirror your reflection would come and take over your body!— XxXAbbeyXxX
- I used to believe that my reflection in the mirror was my evil twin that always had bad hair. XDAnon
- If you stare into a mirror in almost complete darkness, the devil will appear instead of your reflection.Anon
- I used to believe that there was a person in the mirror who looked exactly like meAnon
- I had a fear of seeing a person in the corner of the mirror(most of the time a morlock)— Shane