I also want to link to an excellent on-line essay type thing by John Holbo about the mock-pastoral as exemplified for instance by Don Quixote, Discworld and Galaxy Quest. Also Charlie Kaufman's Adaptation, which is well worth watching by the way.
His argument is that the mock-pastoral is about the simple or deluded (eg the rustic) bringing light to the sophisticated (the urban), about how our mockery is turned on itself, and we learn something from those we underestimated. I can't really do justice to the strength of his argument. He guesses, and he may be right, that writers like Pratchett and Cervantes started off with an intention of simple satire, which he compares to a parasitic plant which takes its nourishment from a stronger tree (the satirised genre). But they took their nourishment from somewhere else: like an epiphyte (a Bromeliad perhaps?) they draw on something real, outside of the genre, which means they now reach out to everyone. No coincidence that Adaptation was about stolen and parasitic orchids.
BRANDON [fan at convention]: Commander, as I was saying... In "The Quasar Dilemma", you used the auxiliary of deck b for Gamma override. But online blueprints indicate deck b is independent of the guidance matrix, so we were wondering where the error lies?
JASON [Tim Allen as Kirk-alike]: It's a television show. Okay? That's all. It's just a bunch of fake sets, and wooden props, do you understand?
But, like the shadows in Plato's cave, the ship is actually physical reality, and later in the film Jason has to phone Brandon and ask him to guide him through it.
Terry Pratchett (Small Gods): ‘Life in this world,’ he said, ‘is, as it were, a sojourn in a cave. What can we know of reality? For all we see of the true nature of existence is, shall we say, no more than bewildering and amusing shadows cast upon the inner wall of a cave by the unseen blinding light of absolute truth, from which we may or may not deduce some glimmer of veracity, and we troglodyte seekers of wisdom can only lift our voices to the unseen and say, humbly, ’Go on, do Deformed Rabbit. . . it’s my favourite.’