The ironic tone is inescapable: “I shall be telling this with a sigh / Somewhere ages and ages hence.” The speaker anticipates his own future insincerity—his need, later on in life, to rearrange the facts and inject a dose of Lone Ranger into the account. He knows that he will be inaccurate, at best, or hypocritical, at worst, when he holds his life up as an example. In fact, he predicts that his future self will betray this moment of decision as if the betrayal were inevitable. This realization is ironic and poignantly pathetic. But the “sigh” is critical. The speaker will not, in his old age, merely gather the youth about him and say, “Do what I did, kiddies. I stuck to my guns, took the road less traveled by, and that has made all the difference.” Rather, he may say this, but he will sigh first; for he won’t believe it himself. Somewhere in the back of his mind will remain the image of yellow woods and two equally leafy paths.
Ironic as it is, this is also a poem infused with the anticipation of remorse. Its title is not “The Road Less Traveled” but “The Road Not Taken.” Even as he makes a choice (a choice he is forced to make if does not want to stand forever in the woods, one for which he has no real guide or definitive basis for decision-making), the speaker knows that he will second-guess himself somewhere down the line—or at the very least he will wonder at what is irrevocably lost: the impossible, unknowable Other Path. But the nature of the decision is such that there is no Right Path—just the chosen path and the other path. What are sighed for ages and ages hence are not so much the wrong decisions as the moments of decision themselves—moments that, one atop the other, mark the passing of a life. This is the more primal strain of remorse.
Thus, to add a further level of irony, the theme of the poem may, after all, be “seize the day.” But a more nuanced carpe diem, if you please.