This is from a comment Susan McLean made several years ago regarding an article by A.E. Stallings called "
Rhyme Driven" --
"Though form does create certain expectations among readers (and form can subvert them, too), for writers, rhyme often drives them places they never expected to go when they started the poem, so the element of chance plays a very large part in the writing of rhymed poems. The minute you write a line that ends with a word you need to rhyme, you start thinking of any possible rhyme word that could pair with it. The unconscious often kicks in and makes a connection that the conscious mind would not have, sometimes even that one’s inner censors might not have let pass otherwise. I often wind up saying things that surprise me, particularly in intensely rhymed poems such as villanelles, in which one really has to stretch to find enough rhymes for the form."
P.S. And from A.E. Stallings, in a follow-up comment: "The rhymes are engine, not ornament."