I like what Nathan Englander is onto here, that the value of "what you know" depends on what end of the telescope you're looking through:
All I know from childhood is I was on my couch watching TV, so I should simply rewrite a whole series of sitcoms for you, I should write a book called What’s Happening and I should write a book called Little House On The Prairie’s On At Five O’clock. That was my childhood experience, and this didn’t feel to me, when I thought of the books that I loved, and the kind of stuff I wanted to write, it felt like I’m going to be very limited by “write what I know.”… Most of the books that we truly love don’t exist because these things did not happen to the people who were writing them. But why do we love those books? Why do they change us? Why do they touch our hearts? Why do they hold so much meaning? Because they are truer than truth, because there’s a great knowing within them. I think what’s behind “write what you know” is emotion, like, Have you known happiness? Have you ever been truly sad? Have you ever longed for something? And that’s the point: if you’ve longed for an Atari 2600 as I did when I was twelve—all I wanted was that game console—if you’ve felt that deep longing, that can also be a deep longing for a lost love, or for liberation for your country, or to reach Mars. That’s the idea. If you’ve known longing, then you can write longing. And that is the “knowing” behind “write what you know.”Englander's talking about fiction writing here, but the implications for autobiography are equally interesting. "Write what you know" is arguably the very basis of personal essaying, but, remember, Montaigne asked the question before he wrote, and he felt his way to the answer, if there was one, and it was usually an affirmation contradicted the next month, year, or decade. The search for "what I know" in an essay, not the essay's ostensible subject, however sexy or statistically abnormal it might be, is the usually the engine. The equation in autobiography is simple, yet confounding: what I know, you know, but you may not know it yet, and I didn't know until I finished. I'm not talking here about arcane pop culture knowledge or a superior intellect; I'm talking, after Englander, of knowing in the deepest sense of human experience, knowledge beyond class, race, cultural origins, gender. If there is such a place, a great essay, a great work of autobiography, will get there as fiction and film can. I think again of what Joyce Carol Oates said: the successful essay "is not place- or time-bound; it survives the occasion of its original composition."