"Excellence is not about balance, it's about extremes." I can't find the source of this quote now, but I think it was Tom Peters quoting someone else.
If you look at any area in which "the world" defines as excellent, and you will see extremes. The divorce rate of US Navy SEAL is 90-95%. Look at the lives of corporate CEOs, for example. Most of their lives are wrapped up in the company. Their divorce rate is a bit lower than the SEALs — 9.8%. I don't see the work-life balance in high-performance people that HR talks about.
Even just aspiring to be world-class requires extremes. For example, if a high school kid wants to be swimming in national competitions, he has to wake up at 4am in the morning to train for 3-4 hours before going to school. More training after. And that's just to try to get into the national level. If you manage to get into the group of folks that train for the Olympics, you don't really have a life outside of swimming. Same for most sports.
My first hand experience doing startups reinforces the point. One of the early engineers I had hired, before starting work, said that it wouldn't be difficult to work long hours. After a few months of 50 hour weeks (making the rest of us think he was a slacker), he came to me and said his wife thought he was spending too much time at work, and he'd have to quit. My friends, 60 hours per week is a light week at a startup. From then on, with every early recruit I had, I made sure that they spoke with their spouses so they understood the commitment they were making coming into a startup. You don't get a big chunk of the company just because you are smart, you get it because you are extreme in your dedication to ensure the success of the company.
A friend with a 15-person startup just said to me: "No one ever told me it would be this hard.".... Almost by definition, there is insufficient time and resources for startups to do all they need to do. The responsibility of the founder is to decide on some of the compromises. If the market evaluates the compromises to be not excellent enough, the company fails. Thus, smart founders push the resources to deliver as much "excellence" as they can. The fewer the compromises, the more likely the product hits the mark, and the more extreme work gets in the startup.
Since Tom Clayton posted Is it possible to be both a founder and a daddy?, I've been wanting to post a counterpoint. It's not that I believe that it is not possible to be both a founder and a dad.... it's that I am clear (as is Tom Clayton) that doing so involves trade-offs. Bringing family life into work, and bringing worklife into the family. Many founders manage to.... some do not (by getting divorced, or by quitting), and many do not have to (by being single).
You get to define "excellence". When it comes to your life and career, there's one saving grace to the situation — you get to define excellence for yourself. But don't fool yourself into thinking you can build a world-class startup by balancing startup work, family, relationships, health, sleep, etc. Usually, something gives. If you choose to be world-class in most "traditional" definitions of work (including being an entrepreneur), then you will have to be extreme to succeed. As far as I can tell, successful entrepreneurs are pretty singularly minded — monomaniacally focused on their startup.
So, the bottomline is that you need to be clear about what excellence means to you. To make your time on this planet count, you need to be clear on: What is your definition of excellence?