If you're a musician, that means playing that most technically advanced piece flawlessly.
If you're an athlete, that means raw ability like speed, strength, etc.
If you're a mathematician, that means having a go at some unsolved/open problem.
If you're in the military, that means joining the special forces or becoming a fighter pilot.
As the author said, when you're young, you often only get judged on one or two objectives. When applying for college, that's GPA and SAT - so you will optimize for those two, and little else.
All this works out for young people, because if there's one thing they tend to have, it is time to grind. And lots of it.
One thing I've noticed with young and ambitious employees, is that many need constant feedback. If they don't get any direct feedback immediately, they feel left out in the cold, and don't know how to react.
Where I work, we often get inquiries from clients, and 80% of the time there's zero feedback. We produce reports / presentations / recommendations, ship to the clients, and that's it. IF we get something back, it is because they want to go forward with something, and need follow-up work.
For the ambitious types that have gotten feedback their whole lives, that can be a hard pill to swallow - it really takes some "unlearning" to get comfortable to work in that environment.