Oz and Ends has a post up called The Dubious Wisdom of "Writing What You Know," in which he quotes four authors on the subject. And what a coincidence! One of them is me!
I'd like to add a little something to the discussion, since I'm the writer quoted who is most in favor of writing what you know--or, as I prefer to call it, writing who you are.
When you write about what you know, you're writing about what other people know because people are more alike then they are different. Shannon Hale said something similar: "people are people." Fiction should take the personal and relate it to human experience in general, just as personal essays do. It's just with fiction, you get to run with whatever personal experience you choose to use whereas with personal essays you're supposed to put up a show about sticking with the truth.
A personal essay-like story to illustrate my point:
Last weekend I was visiting family members in Vermont, including my cousin and his two children, who are in first and third grades. The kids had been reading some of my books. The third-grade girl told me that she was going to keep the Hannah and Brandon book, but she was going to let her younger brother have My Life Among the Aliens because--
At that point, said younger brother broke in, "Because it could have been about me!"
I was incredibly touched, because My Life Among the Aliens deals to a great extent with my experiences as mom to that child's second cousins, who are a great deal older than he is. And, yet, he identified with the Will and Rob of the book to such an extent that he felt that their stories could have been his.
What greater joy can a reader get from a story? What greater joy can a writer get from a reader?