Writing ~ Career Choice or Calling?

I've always been fascinated by First Sale or How I Became an Author stories. Whenever I run across a first sale story, I usually stop and read and I'm always surprised by the ones that say the person simply decided at some point in life to change their profession and become a writer. What's even more amazing is that many of these people never even dabbled in writing until they made a conscious choice to become a writer. And they're successful, otherwise, why would their first sale stories be of interest to anyone? These people went into it as a career choice. Given the wacko, roll-of-the-dice nature of the industry, this blows my mind.

Then we have the other kind of writer, the person with the calling, who is compelled to write stories from a very early age, the person who must write to satisfy the many voices clamoring inside her head. I'm one of those who was compelled to write from the moment I learned to put the alphabet down on paper and form words. Now that I'm getting up in years, I'm not sure whether this is a gift or an affliction.

I think it would be interesting to know the ratio of career choice writers vs. the ones who are simply compelled, when it comes to authors who have successfully "broken in."

Here's the question for today: which are you? Do you write by choice, or have you always felt compelled to write?