In these types of discussions there is always an exception to rule. For example, a first time author writes a best selling book, and obtains an agent and publisher on the first try! Yes, these things do happen, yet for most of us writing and all that goes along with publishing takes hard work. Knowing your subject matter will allow for the learning curve to be a bit smaller.
When my daughter, Christina and I wrote our first novel, I had several failed attempts and a stack of rejection letters to show for my previous efforts, way before she was even born. I attempted my brief foray into writing a best-selling-novel (I never think small), when I was first married and at home with my new baby. After leaving the teaching profession, I was hungry for some type of brain stimulation. Babies are adorable (I've had five), still I wanted something to strive toward. A magazine article caught my eye, with an enticing well written ad piece (of course), about trying my hand at writing in the form of a home study course. (It was a Readers' Digest Course). I was immersed in education all of my life and I loved to learn. I would have been very happy taking writing classes, but at the prodding of the instructor I submitted my work.
It was inevitable that the rejects came, and I was prepared, but it did not lessen the hurt. I sent out a few more and then decided, like any other good life-long learner, that I needed to learn some more. So, began my adventure in reading anything I could get my hands on that taught additional writing skills, techniques, and success stories. Oh, and did I mention I once owned nearly every volume of the latest Writers Market?
Then came my lucky break, a speaking engagement, and then another, and another. Until, the prize speaking engagement, a state convention. I needed a book and fast! I decided to use my teaching skills and pull together a book on the topic of teaching science. It was a hit, currently is in its fifth edition, and was chosen, along with seven of my other titles, in the coveted book on 100 top picks for curriculum. Which brings me back to the original point. For this author, it helped to write what I knew. I taught science successfully in the home and was able to translate my story from complete aversion of the topic as a student, an educator and homeschool parent, to enjoying the subject immensely.
It was five years after my success in self-publishing that my daughter asked me to teach her to write a novel. This was outside of my success scope and so I tried to put her off. Eighty or so pages of typed text reflecting no instruction on transitions, dialogue, setting or plot resulted in a crash course on teaching her to write a fiction novel. We were ultimately successful and upon her entrance to college she had completed three novels. Book number one and book three were set in Florida and in locales we knew well. [I now publish another author's workbook, Susan K. Marlow, on teaching children grades 2 though 8th fiction writing, "Reach for the Stars: Young Author's Fiction Workbook"]