This poem is a villanelle — and the writer has reached for the form with real understanding, because the villanelle is built to do exactly what this poem is about.

A villanelle is a fixed form of nineteen lines: five three-line stanzas (tercets) followed by a closing four-line stanza. It uses only two rhymes across the whole poem, and — more striking — it turns on two refrains. The first and third lines of the opening tercet return, alternately, as the last line of each following tercet, and are finally brought together as the last two lines of the poem, so that the same two lines keep sounding and the poem closes by letting them fall side by side.

Despite its troubadour-sounding name, the villanelle began as a rustic Italian and French dance-song with no fixed shape. The strict nineteen-line form we now call a villanelle was crystallized comparatively late — in the nineteenth century, by poets such as Théodore de Banville, working from a single 1606 poem by Jean Passerat. In English it became a major form only in the twentieth century, in poems such as Dylan Thomas's "Do not go gentle into that good night" and Elizabeth Bishop's "One Art."

What makes the form remarkable is that the refrains return whether the speaker wills them or not — and that compulsion is precisely this poem's subject. A speaker who "told myself I'd left it all behind," yet keeps finding herself "far from cured," is describing relapse, the inability to leave a thing behind; and the villanelle, by forcing its two lines to come back round after round, performs that relapse in its very structure. The form does not illustrate the theme — it enacts it.

The discipline the form teaches is how to make a refrain mean something slightly new each time it returns, so that recurrence becomes development rather than mere repetition — and the seams, where the syntax bends to bring a refrain back into place, are part of the lesson, showing exactly where the line worked hardest.