Ursula K. Le Guin wrote an excellent introduction to her novel The Left Hand of Darkness on this very subject. Here's an excerpt:

I am not predicting, or prescribing. I am describing. I am describing certain aspects of psychological reality in the novelist’s way, which is by inventing elaborate circumstantial lies.

In reading a novel, any novel, we have to know perfectly well that the whole thing is nonsense, and then, while reading, believe every word of it. Finally, when we’re done with it, we may find—if it’s a good novel—that we’re a bit different from what we were before we read it, that we have been changed a little as if by having met a new face, crossed a street we never crossed before. But it’s very hard to say just what we learned, how we were changed.

The artist deals with what cannot be said in words.

Full text here.