"Do what you love" is a great fortune cookie, and a terrible game plan. Countless times when a kid in my class begins to hit a wall and the parents start to consider letting him quit, it because they "don't want to force him".
As someone who spends their entire working life trying to motivate kids, there is nothing I can relate to more than this feeling. But also, I recognize it as a trap.
What they mean is, they don't want to burn diesel forcing them to do Jiu Jitsu on top of all the things they already have to force their kids to do. Brush your teeth, go to school, be nice to your sister, etc...
My whole life has been spent in the world of martial arts, but because of that, I hate the idea that instructors think their students owe them eternal allegiance (and tuition). When a kid steps on my mats, I am excited for them, but I also am excited because I know we will only be together for a limited time. That puts the burden on me to work efficiently and with intention to give them my best as a coach before they move on.
That being said, don't let your kid move on til they get what they signed up for. If you can teach your kid to find a way to do things they hate, they will become unstoppable.
When I was training for karate tournaments in my early 20's, I started weight training for the first time in my entire life. It was an ordeal. I just wasn't used to it. Over time though, I learned to detach my mind from my physical experience. This was extremely helpful because I didn't have to react or care about everything that was happening to me in the gym. I could just go under the wave of discomfort and accept that this was a part of getting what I want.
I think if your life is filled with doing things you hate, then your life sucks. But if your life is only filled with doing what you want to do, you are in all probability not a success.
I think the 80/20 rule is a good metric when it comes to this.
As a teacher of children, I'm begging you to to help your child learn to do things they hate. Its a competitive advantage and one of the clearest signs of character.