I'd go even further to say that this sense of decorum or fittingness must be present for literature to be convincing. In other words, any sense of a lack of adequation with the subject matter is fatal. Of course, there could be cases where readers disagree about whether this quality is present or not. After all, we all have our sense of what goes with what. I'm listening to Oldies on the car radio and a 50s chevy passes me. I feel that this is somehow "right" or fitting. Could Lawrence Olivier do a more convincing Barney Fyfe? I doubt it. Can we imagine a more "appropriate" style for O'Hara Lunch Poems? Doesn't Milton's style "go with" the subject matter of Paradise Lost?

Of course, these connections are man-made, not set in stone. I can imagine an alternate literary universe where things match up differently to one another.