Think for a moment about the different genres of fiction and literature that exist. Everything from historical fiction to urban fantasy to bizarro literature, many of which have a very frail link to "reality." And those who write these genres (well) have no experience in the field. They don't "know" what it's like to be a displaced artificial human or a Revolutionary War soldier or a man who, when he thinks about a particular children's lullaby, has the power to kill people.
And yet, they excel in their writing endeavors.
There is a balance between "write what you know" and "learn what you write." After all, even people writing fiction based on their own lives need to do some research to make sure their facts are right, and that the details are perfect.
So if research is necessary anyway, why would you limit yourself by only writing what you "know"? Instead, why not write what you want, and do the research you need to in order to become an expert in that field?
Perhaps "write what you know" should be altered slightly. Instead of taking it literally (which would mean an entire world full of exclusively realistic fiction), perhaps we should take it to mean that you should inject personal experiences into your writing in order for your readers to connect with the characters and stories. Perhaps it's not what you know from a research standpoint, but what you know from an experiential (is that a word?) standpoint.
What do you think?
Do you "write what you know"? If not, what do you write? Regardless of whether you write what you know or not, how much research do you do in a given writing week?