As a sometime novelist, I have followed his advice. Knowledge can be gained by personal experience or diligent research or a combination of both. J.R.R. Tolkien never received his mail in Middle Earth. But in creating several languages, an alphabet, and a history predating his stories, he damn sure wrote what he knew. It is a popular truism that artists must suffer for their art. There are more ways to suffer than cutting off an ear. The case detailed at the link demonstrates an artists’ suffering is often unappreciated.
Nancy Compton Brophy has been convicted of murdering her husband. Prior to the murder Ms. Brophy was a writer. Here is an example of her work.
There is a perfectly reasonable explanation for why she murdered her husband…. research.