I'm not really sure if i have a valid view on this subject. But what i would do, is to find something or an aspect of life, and use it to enjoy life more and improve it by making it better for others. By this i mean something you are inspired by, or hold very close to your heart.
For example, a couple of years ago i got into long distance walking. The teamwork, friendship, peace and feeling of well being that came from it made me love the environment and everything natural. As a result i'm now interested in global warming, conservation and green issues (i could never have imagined myself being like this a few years ago!), and consequently I want to pursue a career that involves the environment , either safeguarding it, or aiding understanding of it's importance
Thats just how i'd see it, Dunno if ive gone off on a tangent. But the most important thing, is to make a positive effect through whatever your purpose is.