Thoughts on the Human Spirit

So I'm reading this book, Into Thin Air (by Jon Krakauer) for the second time around-- and unfortunately, despite the fact that I am enjoying the book more, the characters' fates are still as un-enjoyable and unfavorable as before. The book winds through an ascent to Everest, and as much as I will it otherwise, 9 people still die, and many others still end up with frostbite. But of the few that remain of these expeditions up the mountain, I'm curious as to how they knew they could keep going, and those many others couldn't. How exhaustion was trumped by the thirst for the summit, how death was somehow trumped by life, despite the clear indications that in all logical situations it would be otherwise. Is this genetic makeup that decided their separate fates that day? Or simply their will?
Let me relate this to my own life. I happen to be a dancer, and tonight I took my average tuesday-night class, variations. For the past month I've learned and rehearsed separate parts of a variation from Balanchine's Who Cares? and tonight we pieced it together, running it beginning to end several times over. It's three or four minutes long, and I realize-- that pales in comparison to many other sports or ventures, such as climbing, but in dance, in ballet, that's long. That's hard.
I felt foolish though, huffing and puffing after running it through for only my second time. Huffing and puffing, mind you, as I thought furiously to myself, you can do this, common now... But what is a limit? What's that word mean? As I read this book and as I dance my part I want to know, when do I know I've pushed too hard, fought too long? Men have climbed Everest. They've spent the night in sub zero temperatures at 28,000 feet, with chilling winds that ripped their clothes off. And I, in my quiet studio that sits midst small-corporate-business-land, is out of breath after dancing for a mere four minutes. So what's up with that? Is that human spirit, should I push harder, work longer...Is that the differentiation in our efforts...I don't know, to be honest.
But what I do know is that I am a human being, precisely engineered for always pushing, hungering for more, more of whatever it is that I need. For me it's dance, for them it was the summit, and although I am fully aware that these two venues are hardly comprable, I've come to the conclusion is that there's always more I can muster, there's always more I can work at, and at least from my viewpoint, I'll never be able to do enough.

I think that's ok though. In fact, it's pretty neat.