This is not me, but my father. We live in a small town with a volunteer fire department and so whenever the fire department is needed, a siren goes off.
Well, one day, I heard a siren that sounded like the normal siren only distant and my father claimed that the neighboring town had a "shark siren".
My mother thought that sounded a bit weird, and then my father realized that he'd probably been lied to as a kid and bought it all his life! (He's 45, so he'd be believing the lie for decades!). He suspected either his parents, or this one friend he's had for a long time were the ones to lie to him.
A childhood belief about lies

others believed things like this
- i used 2 think if u lied your pants would catch on fire cus of the sayin "lier lier pants on fire!"— nell
- When i was child, i used to think my father was my father christmas.— BeB's
- The first time i heard of someone getting fired from a job, i thought that they were actually set on fire.Anon
- at four, I thought my mother was female and me and my father were fee's Anon
- i used to believe that mother and father didn't sleeped— yacine.tah du 91
- one of my friend's was told by his father that if you didn't turn mirrors over the reflection would run out.— pri