As I said somewhere else. I haven't find a definition of my purpose that can really be considered my purpose. But maybe for others is more simple and not so complex.
And purpose changes... because what you want, need, should, can do changes with life... like Steve's purpose went changing as he says.
I think purpose is more like your goals. They go changing. And sometimes you can even define them well. I don't know exactly what my goals are for instance. I take actions in some directions but just because I want to experience that, I'm not sure it will be good things for me.
Like posting here.