Can poetry express the things that a human heart can feel? Are the feelings of the human heart the same thing as the truth? What forms of poetry convey these truths in the most honest manner? They're not easy questions, folks, but when your career has been defined by a soul-searching struggle for the truth in all its forms, it seems to make sense that you'd be willing to talk about the ways that that struggle might not always go smoothly. After all, amidst all the bright lights of stardom, the dangers of national rebellions, and the thrill of love, truth can be pretty hard to pin down. Is Yeats up to the task? "The Circus Animals' Desertion" will tell us, either way.
The myths about which Yeats wrote in his early career no longer ring true for him anymore because they are too neat and pretty. The whole reason the "rag and bone shop of the heart" is "foul" is because it's true, and truth is messy.
Yeats's writing about the human heart won't be any truer than his writing about myths. In the end, the poem suggests that it's all fiction.