Yesterday's newspaper included a cartoon of two cavemen, one of whom is an artist. He is drawing on the cave wall iconic pictures of hunters chasing mastodons, being killed by tigers, running from an unidentifiable but very large beast. To his friend he says, with an air of superiority, "The secret is to write what you know."
This same thing is, of course, told to countless aspiring authors. Many of them follow it slavishly, many pay no attention whatsoever, many run an uncomfortable mental list over their stories and wonder: Should I have done more research?
As with everything else in writing fiction, the write-what-you-know "rule" is a trade-off. Sticking to milieu and situations of which you have some first-hand knowledge can lend stories rich detail unattainable any way else. On the other hand, it can be very limiting if either you don't know much or what you do know doesn't particularly interest you to write about. When I was teaching in D.C., at least half of each class was comprised of lawyers. They all wanted to write high fantasy. And so they should.
Where the dictum is useful is in pulling things from your own life to build on in your fiction. You've never killed anyone (I hope), but you've been angry enough to want to. Can you use that feeling for your murderer? You've never been transformed by a wizard's spell into a toad, but you've felt like an outsider in some social situation: different, awkward, not at home in your own skin. Does the toad person feel like that?
All this floated to the top of my mind when I started a new story this morning. The situation is bizarre, the character unlike myself. But nonetheless there are times where I've felt as he does. In one sense, I know him. Dead mastodons and all.