Agreed all writers say you should write about what you know, but it has to be tempered with objectivity. If not you’re writing a manifesto of indoctrination not a story.

Rowling occasionally has bouts of objectivity and then litters the book with her bitter experiences forgetting that the world isn't made of her bitter experiences and that her views are tainted by her lack of objectivity so carry no weight, they just become embittered unfair generalization.