A brilliant man once said that everything we do, we do because we want to. I somewhat agree.
But, think about this...
Many of us get up every morning and go to work. Is it because we want to? Honestly, I hope that you love your job and can't wait to go to work every day. But for others, they go to work because of what they don't want. The alternative to going to work today may be looking for a job tomorrow... and I don't want to do that. (For the stay-at-home mom's, using the idea of not going to work is just pitifully short-sighted of me... I know... I apologize for the poor example, but I think you get the point.)
So, we use this idea of knowing what we don't want to define what we want. Why not expand the idea and use it on a larger scale?
For anyone out there struggling with the ancient question of "what do I want to do with my life?", one way to answer that is to define what you don't want to do. Define things around you that you see and don't like, things that are unacceptable to you. You may just find a hidden passion of yours.
"It's unacceptable that kids in my neighborhood can't afford school shoes."
"It's unacceptable that violent crime has risen in our city by 10% over the last 2 years."
"It's unacceptable that I have to drive 20 minutes to get a good cup of coffee."
So do something about it.
This idea is not revolutionary... it's not even original. It is, however, often forgotten. So if you're stuck, start defining unacceptable and see where it leads you.