I've never met an adult who said, "I wish my parents wouldn't have made me take piano lessons all those years."
I have met plenty adults, however, who say they wish their parents would not have let them quit.
Musical training - and engaging kids young - has been proven to develop better language and mathematical skills, better spacial intelligence, higher IQ (about 7% higher) and overall greater academic achievement. It also changes the economics of a person's life. And if get your music training young, you create significantly stronger bonds, capacity and never connections in areas that normally deteriorate during Alzheimers and Parkinson's Disease... meaning you have a greater capacity of keeping enough brain cells and healthy connections later in life to prevent or at least reduce the effects of those diseases.
So if you are "forcing" your kid to take piano or another instrument and they want to quit, tell them: "This is not your decision. Just like I don't let you quit school on those days when you don't feel like attending, I'm going to make this decision for you now... and you'll thank me for it later."
Maybe bet them $100 that they'll one day thank you.
You can collect on that bet when they're 25... the same year they have a fully developed pre-frontal cortex (adult brain).