I used to believe "write what you know" meant one should only write things autobiographical in nature—and a cursory glance at the fiction section of any bookstore or library amply demonstrates the falsity of this.

More recently, I've come to realize what it really means. It means you should write based on your experiences. Is a character in love? Don't describe it with cliches, or what you think your readers expect; instead, draw on your own experiences of being in love. Obviously it won't be an exact fit (unless you are writing autobiography), but it's a starting point. The same goes for other emotions and even interactions. You have a mother (probably), so you needn't lean on your imagination in determining how the character interacts with his or her mother, even if the character has three heads, six arms, and nine sets of genitalia.

Another overlooked application of this maxim is research. Anything you've learned through research, you know. If you want to write about the New York draft riots, you don't have to have lived through them, which is just as well, since they were in 1863. People who did live through them kept diaries, penned letters, and wrote books, and you can read them at your local library, along with the work of historians who themselves have pored over these primary sources. Once you've learned about it, why, it has invisibly become something you know.

Surely Douglas Adams, Terry Pratchett, Isaac Asimov, Walter M. Miller, Jr., and Ray Bradbury wrote what they knew, and they clearly weren't writing autobiography.

After all, applied to noding, the philosophy as commonly understood would result in little else but GTKY nodes.