I have been blessed with the joy of being able to choose many of the projects I have been involved with. My project-selection criteria hasn't always been the best. 

Early in my career, technology was my main motivation. In one project, I had built the best mousetrap in a world where there were very few mice to catch. Oh, so the market need is important !

Over the course of the many ups and downs in my entrepreneurial life, I was able to refine said criteria. This graph that I found floating on the Internet sea best describes it. (click to enlarge)

It's not always possible to find the 'Bliss' sweet spot (OK, truth be told, it's very rare), but it's something I consistently aim for. And if I can't have 'Bliss', at least I know where I am and why I am doing it.