A childhood belief about general

I used to believe that people had one good ear and one bad ear. I couldn't hear in my left ear, and I thought it was completely normal. Then one day I saw my older sister switch the telephone receiver to her "other" ear! I was completely stunned! I must've been in second grade and I could not understand how she could do that. I asked my mom, and she explained to me that I couldn't hear in my left ear because of an ear infection years earlier...