"The Only Thing You Really Care About"

I like this quote from an interview with Philipp Meyer, author of a novel I just finished (American Rust -- see my review here):

"Really, you just have to keep writing and ignore the thousands of rejections that accumulate along the way.  Aside from being a good person, and treating your family and friends well, writing has to be the only thing you really care about.  Once you start feeling this way, regardless of what anyone else thinks, you're a writer."

So, my question is, what is the one thing that you really care about?  Is there something that defines you in terms of your career or occupation?  Is it something spiritual, like a relationship with Jesus or a particular idea about faith?

I wouldn't say I have a single defining interest or activity.  I am clearly interested in politics, and I love reading and writing, but I wouldn't say that defines me.  I would say my love for God defines me.  That can be a very vague concept, but for me it comes down to some practical decisions about everyday life.  Just some deep thoughts for this evening...where's Jack Handy when you need him?