Sister tells her brother that his daughter isn't a piano prodigy after she said she wanted to quit the instrument, he accused her of being jealous of his daughter: 'She's a regular kid who's learning an instrument, not some once-in-a-generation talent'

Your kid is not some kind of music prodigy. She just takes classes. If she wants to stop taking those classes, the least you can do is hear her out. 

Some parents love to force their child into something that they like, but not necessarily something the child enjoys. That is fine in some cases, for example, with school. Even if the kid hates to go to school and have an education, they still need to go and continue to learn. In that case, it is perfectly understandable that a parent is forcing the child. The problem comes when that translates into other areas. Sometimes parents would want their kid to be really good at something in particular, like piano, pageants, or even rugby. Whatever it is, this usually comes with a lot of expectations on the child to succeed in said activity. They have to do it, but not because they show an interest in that activity, but because their parents want them to do it. That is not as good as it sounds. It seems like those kinds of parents do not care whether their child wants to play soccer, is good at it, or even enjoys the matches. They just care about the fact that they want their child to succeed in it no matter what. 

That kind of expectation, when put into a child, can cause a lot of damage to their development. I'm not saying that your kids should be able to always pick and choose what they want to do. It's not black or white. But I do think that if a kid continues to insist on how much they hate doing a certain activity, the least you can do is hear them out. Hear their complaints and take them into account. Maybe they don't even fully hate the activity, but they are tired of going to classes after school. Having expectations on you child isn't inherently wrong, it could guide them into a certain direction and mold them to be the best version of themselves. But that doesn't mean that you should have a lot of expectations deposited into a child that is just trying to live their life. You cannot live through your son or daughter; you can guide them, help them, and teach them, but they are not you. So maybe it's normal that they don't want to do the things that you like, and instead they want to discover what they like.