It can be a mistake to write what you know if you try to include exactly what you know.
I'll give you an example.
I'm working on a novel now that includes a scene in a small chapel. It would be easy to get off track by trying to describe that room as it truly is (at a local church near here) but the book doesn't need that. I can move a door or change the seats to pews or make a dozen other modifications if that's better for the story.
Being too exact, too precise, with reality can clutter up what you're really trying to do. And, as Willie and I point out in "How to Write Your Novel in Nine Weeks," if you try to get all the details 100 percent correct, you'll never finish the book.
The reality changes. Takes what's useful and make up the rest.
The sock and I talk about that in this podcast: