[John Isbell]

I'll just agree with AZ on the point that for much of the history of literature, over much of the planet, originality was not at all what writers and their audiences seem to have expected. In the European tradition, with which I am least unfamiliar, this is true from Aeschylus to Virgil to Marie de France to Racine. Yeats's "When you are old and grey..." is, for a good half of the poem, Ronsard.
That point seems worth making in this discussion.

True wit is nature to advantage dressed;
What oft was thought, but ne'er so well expressed.

Cheers,
John