Imagine if J.R.R. Tolkien had adhered to the advice: "Write about what you know"? There would be no Middle Earth, no hobbits, no Gandalf... Not only would an entire genre of literature fail to exist, but I'd bet my eye teeth many of the great books we know today would never have been written.
Really, who spawned this suffocating notion that we must first be experts in a given field to write about it? Perhaps the better advice would be to write about what fires your imagination and what you're so passionate about that you could bury yourself up to your elbows in reference material for days on end?
I've been asked many times why I write about medieval times or certain figures like Robert the Bruce, Owain Glyndwr, Queen Isabella and Roger Mortimer. The seed of my fascination began with a childhood spent reading Ivanhoe, The Three Musketeers and a plethora of Jean Plaidy books. But spare time for reading died with college and children.
Then, I saw the movie Braveheart. Yeah, yeah, yeah - you historical accuracy purists who so readily decry its inaccuracies may clamber down from your soapboxes for a moment. Truth is, I had never even heard of William Wallace before then. Never. And I only had an inkling who Robert the Bruce was. Yet because of that Hollywood-ized version of a historical era, I was so inspired I wanted to learn more. It re-ignited my love for history and reading and a dream I'd had since I was 12 - to write. Not about something I knew, but something which inspired me: the struggle for freedom, the weak overcoming the strong, hope, persistence, loyalty --- all of it lying in wait in history's chronicles and waiting to be told to new generations.
The fun part about being a writer is that you learn so much in the process. And when that research shows, so will your readers!