Write what you know is some of the most commonly given writing advice. It's good advice. A story is more authentic if the author is writing from their truth.
I often don't follow that advice. If I did all my stories would be about a middle-aged woman that complains about everyting having to be open concept on the HGTV shows she watches like an addict. Am I really the only person that has dirty dishes in the kitchen sink that doesn't want people to see as soon as they open the front door While I've had many experiences and a few different careers, I don't have enough to make characters that vary. So, sometimes I have to write about careers or places I know nothing or very little about. In the case of Someone to Love, I had to write about beers I've never tasted.
Writing about those unknowns is expected from any author. But as a romance author I have to write about some other unknowns. If I were to write only what I know about live, it would be a mixture of funny and boring, with a pinch of sad. That's why I write what I want instead. I write about the various types of men I wanted and the way I desired to be wooed me when I was single.
It's not just the men and the romance, it's also me I want to be. My heroines are often the more perfect woman I wish I were in my heroines. They are still flawed. I write my flaws, past and present, into them but they get the chance to grow and over come them. This makes the characters more three dimensional and relatable.
In a way, I am writing what I know because I know what I want and who I'm striving to be. Write those things that are so instilled in you they're second nature as well as what you dream about.