My brother thinks he was naturally better than me at chess from childhood. He tells everyone he started beating his older brother when he was only eight. What he doesn't know is that after our parents separated, chess was one of the few things that made him genuinely excited, so I started making small mistakes on purpose.
The problem is that somewhere around age 15, he actually became much better than me. Now I couldn't beat him even if I wanted to. He is 24 and still brings up his legendary childhood victories. I will take this secret to my grave because his confidence during those years was worth more than my pride.