The most concise way to break down the good and the ugly of the trope “write what you know” is this two-minute video of author Nathan Englander extolling the virtues of the phrase, while also pointing out how people unfortunately get it wrong most of the time.
As Englander notes, he was a suburban kid who spent a lot of his life watching TV. He didn’t live in Buenos Aires during the Dirty War, as he wrote about in The Ministry of Special Cases, nor was he told by a rabbi to visit a prostitute in the title story of his shorts collection For the Relief of Unbearable Urges. So how can he be such a firm believer in the phrase when he is clearly writing about things he has no experience?
It comes down to, essentially, empathy.
Or rather it comes down to not knowing what it means to live in South America in the 70s, but what it means to be afraid. To worry for yourself and your loved ones. To feel that there is something powerful you can’t get out from under. Englander writes what he knows by taking these emotions and then giving them to a character. He understands that regardless of time or place, humans are guided by certain hopes and fears and loves and lusts.
Angelina Jolie once said that the way she gets into the heads of the characters she portrays is not to take on a completely alien persona, but rather she identifies the part of her personality that she shares with the character and then amplifies it. In this way she is writing what she knows, whether she is a hacker or a witch or a tomb raider.
A different way to approach this is the phrase “specificity equals universality.” The most personal and peculiar thoughts about yourself and the world are actually more likely to be shared by others. And this is where the best work comes from.
Writing how you think everyone feels usually falls flat; but writing those things buried deep under the surface touches many, many more.