"I'm no good at math."
I must have heard this come out of my daughter's mouth a thousand times over the years. When she was in primary school, she would hide behind the curtains and cry when it came time to review her math homework. She hated it so much, and there was no convincing her otherwise.
Do you remember this 1970s Crackerjack TV ad? (If you don't, then just watch it. That's why I embedded it. You're welcome.) "Whaddaya call a kid who can swing like that? You call that kid a Crackerjack."
This ad popped up repeatedly during Saturday morning cartoons when I was a kid, and jealousy would surface. I would bitterly think, "What's wrong with me? How come I'm not really good at any one thing? I'm not a Crackerjack kid." I certainly wasn't that girl in the ad: I took gymnastics, and while I managed to learn how to do an aerial, I never could master a back handspring or the uneven bars because my arms were too skinny and weak.