Because the poem isn’t “The Road Less Traveled.” It’s “The Road Not Taken.” And the road not taken, of course, is the road one didn’t take—which means that the title passes over the “less traveled” road the speaker claims to have followed in order to foreground the road he never tried. The title isn’t about what he did; it’s about what he didn’t do. Or is it? The more one thinks about it, the more difficult it becomes to be sure who is doing what and why. As the scholar Mark Richardson puts it:

Which road, after all, is the road “not taken”? Is it the one the speaker takes, which, according to his last description of it, is “less travelled”—that is to say, not taken by others? Or does the title refer to the supposedly better-travelled road that the speaker himself fails to take? Precisely who is not doing the taking?

We know that Frost originally titled the poem “Two Roads,” so renaming it “The Road Not Taken” was a matter of deliberation, not whim. Frost wanted readers to ask the questions Richardson asks.

More than that, he wanted to juxtapose two visions—two possible poems, you might say—at the very beginning of his lyric. The first is the poem that readers think of as “The Road Less Traveled,” in which the speaker is quietly congratulating himself for taking an uncommon path (that is, a path not taken by others). The second is the parodic poem that Frost himself claimed to have originally had in mind, in which the dominant tone is one of self-dramatizing regret (over the path not taken by the speaker). These two potential poems revolve around each other, separating and overlapping like clouds in a way that leaves neither reading perfectly visible. If this is what Frost meant to do, then it’s reasonable to wonder if, as Thomas suggested, he may have outsmarted himself in addition to casual readers.

But this depends on what you think “The Road Not Taken” is trying to say. If you believe the poem is meant to take a position on will, agency, the nature of choice, and so forth—as the majority of readers have assumed—then it can seem unsatisfying (at best “a kind of joke,” as Schulz puts it). But if you think of the poem not as stating various viewpoints but rather as performing them, setting them beside and against one another, then a very different reading emerges. Here it’s helpful, as is so often the case, to call upon a nineteenth-century logician. In The Elements of Logic, Richard Whately describes the fallacy of substitution like so: