Write what you know, we have all heard it many times before. Write what you know. What does writing what you know really mean? I have met a lot of younger writers who have heard this in school or from a more senior writer or some random Internet bloke posing as a writer. It is a piece of advice that is given out just like show don’t tell. It’s a pejorative at best for most.
I have seen people take it to mean that you should not write about things you don’t know about. For instance, if you are white writing about a black character. Clearly, that is a violation because you cannot know what it is to be racially different than your birth race. I have heard others take as meaning don’t write about things like science if you don’t understand science.
I think all these are not productive takes on it. Write what you know is the call to adventure! Be a brave writer! Be brave and live out the heroes journey and learn as much as you can. Then write what you know!
It is about researching your topics in your stories. If you don’t know what a busy subway is like cause you were raised in the country maybe go visit a city and experience one. If you don’t know about medical history look it up online. Know what your character would know. Don’t be an expert but learn how to pose as if you are.
I think writers come off as smart because a writer is an ultimate pretender. We are able to wear the skins of whatever we desire. We rip the souls of others out of their bodies and place it into the puppets we act out on the page. This means we must experience and know as much as we can. That is the mastery of write what you know. If you don’t know, go make it known.