Like many others, I've always been suspicious of that old writing-workshop saw, "write what you know." Unexamined, it tends to lead to lots of stories about undergraduates at keg parties (if you are an undergraduate writing major), or about writers with writers' block (the rest of us). It discourages us from ever leaving our comfort zones and, god forbid, learning about other kinds of people or experiences. And if fiction writers aren't willing to explore, then what is the world coming to? Well, it becomes a vast blank space in which tiny, disconnected voices cry out for attention--without doing very much to earn it.
On the other hand, it has lately dawned on me that the stories I've written that seem most successful--both in terms of others' responses and my own feelings about them--*are* about what I know most intimately. True, and somewhat contrary to the rant above, they tend to have some external autobiographical elements. But what those elements have actually achieved, without my conscious intention, is to draw emotional authenticity into the story. I set up these trappings of self, I thought, out of laziness: why do research on, say, men who work on oil rigs, when I already know what it's like to be an underemployed, nearly ex-academic? Knowing the external context, though, is what allowed me to depict the emotional experience that became the heart of the story. I know not only how ex-academics looking for meaningful work spend their days, I know what it feels like to be in that position, and what kinds of awkward, bizarre emotional adventures can--or might--ensue when one is in such a state. Those experiences made readers (and me) care.
This doesn't at all mean that one can't or shouldn't branch out from one's own literal experiences. Quite the opposite. But I do think it helps to have some kind of authentic, *emotional* anchor--even if it's only visible to you--in your story. Maybe include a character based on your passive-aggressive father, only with a completely different job, or an interlude that reminds you of the time you thought your dog had run away for good. Even if the rest of the story is invented out of whole cloth, that anchor can be a wellspring of emotional authenticity for the whole enterprise. It helps ensure that you are writing what you know emotionally, and that, I think, is what we really want from stories.