I'd add location as a 4th item to Chris's list of 3. You can have the best job in the world, but if you hate where you live you'll always be looking for a chance to move someplace else. I currently "work" for a non-profit and I don't do it for money, the people are nice, the work isn't really great, and the location is 1500 miles from where my wife would like to live. We made this choice because we believe in what the organization does. It isn't a job it is a ministry for us. Does that mean we'll never leave it, no. Does that mean I want to get up and go to the office every day, no.

At the end of the day I want to see that my work is having an impact and if it isn't then that is when I am looking to move on.