This is the quote I was referencing a few posts back, from Anthony Lane:

“Many of the writers on this [Top Ten] list are under the impression that if they do the factual spadework, the fiction will dig itself in and hunker down, solid and secure….The effect…is quite the opposite.  It suggests that the writers are hanging on for grim life to what they know for fear of unleashing what they don’t know; they are frightened, in other words, of their own imagination….When Flaubert studied ancient Carthage for ‘Salammbo,’ or the particulars of medieval falconry for ‘The Legend of St. Julien Hospitalier,’ he was furnishing and feathering a world that had already taken shape within his mind[.]“