Everyone has a shelf life.
You can increase your shelf life with balance.
In this case, Bethany is an elite crossfitter and she increases her shelf life by building her post-crossfit life on the side. She leaves it all in the gym. She puts the work in, she gets out. Serious focus day in and day out takes a toll on you mentally and you need those side hustles or hobbies to decrease external stressors and the like. Learn how much you can push yourself every day and the time you have away from the grind, use it to build other things. Who knows, if you’re one of those people who can focus on one task for 18 hours a day for 15 years, great! If not, 17 is fine too. 14 is also fine. Same with 8. Learn what you can manage and be intense for those hours. You’ll get a lot more done than someone spending 18 hours inefficiently.
24/7 focused on one thing might feel great short term, but long term, it could be the fastest way to ending your career. Be the hardest worker, but also be the smartest worker.