I've been thinking about this because I recently spent yet another magic morning in the library doing research for the novel, stressing out about historical realism.
As I was walking out of the library, I thought of another metaphor to add to my previous discussion of the problem. It's like trompe l'oeil. Think about it: a representational painting creates the illusion that you are seeing into space (the much-vaunted "picture window"), but at bottom it is still just an arrangement of lines and shapes and colors on a flat canvas. Trompe l'oeil is the most extreme example of this principle, striving for an illusion that borders on trickery.
It's the same with historical writing: I want to make my reader think (s)he's seeing into history --- and to do so I'd better look at history pretty darn closely and replicate it as nearly as I can --- but the very nature of my project is illusion and craft. That's the nature of the beast.
And aren't the best stories, that pull us in and wrap us up, a form of trompe l'oeil? Why do we cry when Romeo and Juliet die, if there's not a part of us that thinks they seem real?