In terms of fiction, which is what I think of most of the time, there are two main types of writers.
First are those who always wanted to write. They may have taken more financially secure career paths, but never lost sight of their desire to be writers. The others of that group went the direct route, realizing they might have to do other writing jobs until their fiction career took off.
The second group fell into writing. This is the group where I belong. While I did take writing courses in high school and at university, it was never my goal to be a writer. Think about it - what makes sense of a dyslexic person being a novelist? At any rate, with this group, eventually an overwhelming desire to write befalls them and they write.
I've heard a number of people say they wrote as therapy for a situation in their life. Some write as a hobby that fulfills a creative outlet. Others have an internal awakening of a desire to be a writer. By now, everyone must know how I transitioned from a reclusive hobbyist to a public writer.
I've read on forums advice to write to please oneself. While I wholeheartedly agree that one must be true to themselves, it is not necessarily good writing to write for one's own satisfaction. Writing to the industry means that by the time the ms is ready to shop, the interest in that genre might have passed.
My formula for writing is to be true to the characters and tell their story, not to myself, but to the eventual readers. I deliberately added elements with specific readers in mind (my friends and family). Using the statistical theory of a sample being representative of the whole, I figured these people - very different from each other - represented different sections of the fiction reading population.
In retrospect, it worked because people who typically would not have interest in my books reported back the way they were touched by Kathryn. She became real to them. She spoke to them and for them, sometimes things they could not say. The biggest surprise to me was that men didn't hate my books and actually finished reading them.
The point is to write to the readers. That is the art of writing. The craft and industry are simply tools of the trade.
Read some of the comments here. http://nadinelamanbooks.com/reviews.html