We are all familiar with the old adage, “Write what you know.” This concept is loosely attributed to Hemmingway, and for two reasons. One, he had a habit of writing about things he did. Watch bull fighting, writing a couple of books about bull fighting. Go to war and like fishing, write stories about war and fishing. The other reason, however, is that in A Moveable Feast he discusses making a decision to write a story about one thing he knows for sure. It is easy to think that he meant something he had experienced personally, but I believe in this instance he was referring to what he knew to be true.
And this is all any writer could and should do. After all, many writers will be called to write about things they have never done. There are entire genres—science fiction, fantasy, perhaps romance—where this is the case. But the doing isn’t the point. What matters is what you know.
I think it was Carl Jung who said, and I paraphrase, “I don’t believe anything. I either know it or I don’t.” I like this, and it’s a good motto for a writer. Believing is hedging your bets. Know what you know. Claim it. And then write about it. It doesn’t matter whether that story is set in 21st century Seattle or on Gallagon Nine, your story will always be better if it is built on the bones of what you know in your heart to be true.
And if some day you decide something different is true, so be it. You can only know what you know at the moment. If you wait until you know absolutely everything before you write a book, you will be one very old first-time novelist indeed. So stake your flag. Choose one thing that you know for sure and write about it. And people will either agree with you or not—that’s none of your concern. Your only concern is finding the next thing you know for sure.