I'm glad OP posted this. I'm actually a bit surprised this sentiment hasn't been expressed more often, but I guess it's part of the bubble a lot of Valley entrepeneurs live in. I am just a 25-year old guy working as a regular employee in a small consulting company with flexible hours and freedom to take unpaid leave pretty much whenever I feel like it, but I have some pretty strong opinions on parts of the startup culture.
To be frank, it seems like a lot of startup employees suffer from OCD (literally). Working really long hours and improving the product, changing the world etc. is what it's always about. Lots of people seem to lose sight of the ultimate goal in life, which is being happy. Or maybe they didn't have a goal in the first place, and working really hard is a substitute for something else which is missing in their lives.
Unhealthily hard work is a good idea _for a period of time_, if it _seems as if it's working_, as a means to an end: Making a lot of money in a few years instead of throughout a lifetime, creating something of your own and leaving your mark on the world, reaching your true potential, etc. But if you're working 12 hours a day for _years_ with nothing to show for it, you are on the wrong track and should take a step back.
I realized this after experiencing burnout at 19, spending two years where I was capable of doing absolutely nothing traditionlly productive. Therefore, it's really surprising to me that a lot of supposedly older and wiser do this rat race for years, losing sight of the goal along the way.
Pushing really hard to achieve something great is a huge risk to your mental well-being, and this is something you should go into with both eyes open. It's better to make a tactical retreat if things seem too hard.
You can be perfectly happy not being a Steve Jobs. In fact, if it doesn't come naturally, you're almost guaranteed to be happier by being a little easier on yourself.