Our speaker is a poet. Yeats is a poet. Our speaker is a man nearing the end of his career. Yeats is nearing the end of his career. Our speaker spent a good deal of his life invested in Irish mythology. Yeats spent a good deal of his life invested in Irish mythology. We're sensing a pattern here…
We know that it's usually poor form to confuse the author of a poem with its speaker, but it's a pretty fair bet that they are pretty close to the same thing here. Here's our evidence:
(1) For starters, Yeats's early work rarely featured a first-person voice. After all, when you're describing "Leda and the Swan" or "Sailing to Byzantium", chances are that you don't need another voice to interfere. It's best to just tell the story, right? The fact that Yeats liked to keep his distance means that "The Circus Animals' Desertion" reads as an especially personal and intense poem for him. It's an honest appraisal of Yeats's own creative past. The "I" who declares himself as a struggling writer is one who doesn't often appear in the pages of Yeats's other works.
(2) Yeats also spent a good deal of his energy on two projects: love and poetry. Like the speaker, he managed to get drawn into some of the fiercest battles of the Irish rebellion – and he reflected those experiences in verse.
So why turn to such an intensely personal voice now, at the end of his career? After all, Yeats was about as popular and well regarded as any poet has ever been (or ever will be), and he gained that reputation while writing with very distant speakers. Perhaps, though, he felt that he was out of characters to trot out on stage. When all is said and done, the only thing anyone can be sure about is his own heart. And that's what our speaker chooses to concentrate on.