Writing what you know is not always what you think
Who hasn't heard that old adage, "write what you know"? That's how to get realism in your story, and if your story doesn't feel real, nobody's going to want to read it, goes the thought. Oh poor writers, sitting there with that sinking feeling, because you're an accountant or a phys ed teacher and you want to write hard science fiction or steampunk, but the adage says you can't.