Navel-Gazing in August
Someone said "write what you know." It was definitely Mark Twain, Ernest Hemingway, Nathan Englander, or somebody else.
I've mostly seen the quote applied to writing fiction.
Apparently some folks assume that it means authors should only write stories about events they've experienced. That may help explain why fantasy and science fiction stories aren't taken seriously in some circles, and entirely too seriously in others.
Others, including John Briggs, Diablo Cody/Brook Busey-Maurio and Jason Gots, say it means using the author's emotional memories when telling stories. They're professional writers, so I figure they know what they're talking about.
More at A Catholic Citizen in America.