If the title were "No Second Chances," it could make a great motivational poem to read at halftime of the big game...
But, no, the real title, "No Second Troy," alludes to ancient Greek history. Hot. The destruction of Troy, as depicted in Homer's Iliad and Virgil's Aeneid, is perhaps the most famous epic event in Western literature. Yeats knew his Greek history inside and out, and so we're not too surprised by his choice. (Check out his poem "Leda and the Swan," which also deals with Greek history, on Shmoop).
Funny thing is, neither Troy nor the ancient Greeks are mentioned specifically until the last line of the poem. By the end, the reader is expected to know that Yeats is comparing the female figure in the poem to the notorious Helen of Troy. The title is something of a joke: the speaker is saying that if there had only been another Troy to burn, Maud Gonne wouldn't have needed to cause so much trouble in Ireland. Sadly for the speaker and his country, there are no ancient cities lying around in need of a good burnin'.