Proust has written with great penetration of the difference between the writer as writer and the writer as a social being. You will find his thoughts in some of his essays in Against Sainte-Beuve, a book reconstituted from his early papers. The nineteenth-century French critic Sainte-Beuve believed that to understand a writer it was necessary to know as much as possible about the exterior man, the details of his life. It is a beguiling method, using the man to illuminate the work. It might seem unassailable. But Proust is able very convincingly to pick it apart. "This method of Sainte-Beuve," Proust writes, "ignores what a very slight degree of self-acquaintance teaches us: that a book is the product of a different self from the self we manifest in our habits, in our social life, in our vices. If we would try to understand that particular self, it is by searching our own bosoms, and trying to reconstruct it there, that we may arrive at it."
Those words of Proust should be with us whenever we are reading the biography of a writer - or the biography of anyone who depends on what can be called inspiration. All the details of the life and the quirks and the friendships can be laid out for us, but the mystery of the writing will remain. No amount of documentation, however fascinating, can take us there. The biography of a writer - or even the autobiography - will always have this incompleteness.
