Do what you love
A little over 10 years ago, I was a process engineer at a large company. I really liked my company, but really hated my job. I think the thing I hated most was that I didn't feel challenged. I often felt like college was a complete waste, and that I could have done my job out of high school. I think I also didn't like the fact that the amount of work performed seemed irrelevant. So a coworker who spent pretty much eight hours a day talking about football and one hour working comes off about the same as me who spends eight hours working. Why couldn't I just do the one hour and go home? Anyway, this whole debacle (among other things) led me to a period of sadness in my life.
It was my husband who saved me. He asked me to evaluate all the things I had ever done in my life in school or as a hobby. Rather quickly, I told him that my favorite thing was research and that I thought I wanted to teach. It's kind of difficult to go back to school after being out for two years (and making $$$), but it was really what I wanted. I think graduate school was a little easier for me because I was "doing what I loved." I was willing to quit and try something different if it ever got to crazy, and so I never worked the 80 hour weeks, because that wasn't what I "loved." Yet, I still graduated, still got a faculty position, and here I am now doing ~ 45 hr weeks and I think I am doing just fine.
Now, my husband faces the same question. He just finished his MBA and tried to go back to his pre-MBA field in -ology. Turns out that he hates -ology. Now, he is trying to start a company. This is a little risky because we don't expect a revenue stream (i.e., salary) for some time, but it doesn't really matter because I am working. He is "doing what he loves" and he couldn't be happier. It can be scary to take a risk like quitting a job to go back to school or to start a company, but it is always worth it to "do what you love."