That's sad. There are so many factors at play. I would say that with my friend and his daughter, one of the reasons it worked out well was because they spent so much time together: traveling to competitions, driving to the mountains for skiing every weekend. They enjoyed each other's company and bonded over these shared experiences, and things like introducing her to the Beatles and the Grateful Dead.
> They enjoyed each other's company and bonded over these shared experiences
My son competes on the national and international level in two different sports, so we do a lot of traveling. The bonding is very important, just as it is knowing when to get out of the way and let them shine.
In one sport, I drop him off and pick him up for practice (he gets distracted/flustered when someone is there watching him practice). In the other, I practice with him and am trying to stay better than him as long as I can.
There are a few other things I think are important...
If they don't want to do something, don't push them to. My son decided not to compete in a national ranking event in a couple of months because his competitions are on Thursday and Saturday and he would miss three days of school when factoring in travel.
Try to anticipate their eventual needs and make sure the right tools/equipment/etc. are available for them before they realize they needed it. Also, have backup equipment just in case something breaks or fails.
Make sure that they understand the 'why' behind all the things that both they have done, and what you have done, to enable them to get to that level.
Finally, from a young age, teach them to "always do your best, and always do better next time." The first national competition he went to, he literally finished dead last out of over 250. When we were in the airport heading home, I let him know that it's alright if he doesn't want to do more of them. He didn't back down in the slightest, and asked me when the next one was because he knew he could do better. Next month will be the second time he competes in the Junior Olympics for that sport.