They say "write what you know", and really, "they" are pretty good at saying things that sound simple and make sense . . . until you start trying to do it and suddenly you find yourself asking, "What the heck does that mean?"
First off, how can you write something you don't know? I mean, take a look at that statement. If you write something, you have to know it . . . because if you don't know it, it's not in your brain, and you can't write it. You may not know MUCH about what you're writing, but that is easy to remedy: through research you can learn about something . . . but knowing ABOUT something is not what "they" are talking about. I think.
I believe when they say "write what you know" they mean this: when you write, dig deep. Connect with each of your characters, by doing what some people may call "method acting".
Recently, I've been trying to apply "method acting" principles to my writing. "Classic Acting" (my term, I think) is when you simulate emotions as you act a part. You simulate laughter, you simulate weeping, you simulate the feelings you are portraying. And some actors are quite good at this. "Method Acting", on the other hand, is where you actually draw upon those emotions so that in the moment you are acting, you are feeling those feelings. Instead of just acting sad when you play the part of a girl who just lost her puppy, you draw on your own memories of that day when you found out your kitten was run over by a snowplow. Instead of just going through the motions of laughing when another character tells a stupid joke, you bring up your own memories of that day when you found out your best friends kitten was run over by a snowplow. You get the idea.
"Method Writing" is the same idea. When writing about a serious tragedy or writing about a personal triumph or writing about a introspective realization . . . you bring these emotions up from your own well of experience. This is where you beging writing what you know in earnest, not just writing what you know about! This is where if you spend all your time cooped up watching movies or reading comics, you aren't going to be a very effective writer because you aren't experiencing life! Your emotional experiences are limited to what you see in front of you, not what you feel.
Feelings are what connects people. Love. Passion. Happiness. Silliness. Pain. Sorrow. Unless you are a callous person with no soul or are experiencing overwhelming emotions of your own, if you see someone experiencing these feelings you will be empathetic to the person who is feeling these emotions. You will connect with them, based on your own experiences with these feelings. You speak with a lovesick teenager . . . you'll remember your own embarrassment when you felt that way, and maybe even be slightly annoyed with them -- but that annoyance comes from empathy. You speak with a heartbroken teenager . . . you'll remember when your own heart was broken, and either feel bad for them or, again, annoyed. But these feelings come from shared experiences. Someone tells a joke that's not all that funny? You may find yourself laughing simply because other people are.
Art has a dual purpose, although these purposes often wrap around each other. It can be cathartic, a way to sort through feelings on an internal level; or it can be to connect one soul to another, on an external level. This is why I "preach" about the power of art, and why it bothers me when I see people minimizing art as "it's just a story" or "it's just a joke". No. It is a connection between two souls. Or two brains, if you don't believe in souls. Whatever, the concept is the same. It's an interpersonal connection.
To truly connect, though, the story must FEEL true! It must feel right! It must feel recognizable! Art is a caricature of real life, and as a caricature it must be something people can look at and see recognizable features.
So, writers, dig deep. Work hard to make your stories and characters as emotionally "true" as you can. Doing this will cause a connection between your reader and your characters . . . and --this part is scary -- you.
The only way you can do this is to get to know your characters . . . and get to know yourself . . . and then, "write what you know".
Samurai art by Tim Baron, (c) 2009