Frost spent the years 1912 to 1915 in England, where among his acquaintances was the writer Edward Thomas. Thomas and Frost became close friends and took many walks together. After Frost returned to New Hampshire in 1915, he sent Thomas an advance copy of "The Road Not Taken". Thomas took the poem seriously and personally, and it may have been significant in Thomas' decision to enlist in World War I. Thomas was killed two years later in the Battle of Arras.
"The Road Not Taken" is a narrative poem consisting of four stanzas of 5 lines each in iambic tetrameter (though it is hypermetric by one beat - there are nine syllables per line instead of the strict eight required for tetrameter) and is one of Frost's most popular works. Besides being among the best known poems, some claim that it is one of the most misunderstood.
Frost's biographer Lawrance Thompson is cited as saying that the poem's narrator is "one who habitually wastes energy in regretting any choice made: belatedly but wistfully he sighs over the attractive alternative rejected". According to the Thompson biography, Robert Frost: The Years of Triumph (1971), in his introduction in readings to the public, Frost would say that the speaker was based on his friend Edward Thomas. In Frost's words, Thomas was "a person who, whichever road he went, would be sorry he didn't go the other".
While a case could be made for the sigh being one of satisfaction, the critical "regret" analysis supports the interpretation that this poem is about the human tendency to look back and attribute blame to minor events in one's life, or to attribute more meaning to things than they may deserve. According to biographer Lawrence Thompson, as Frost was once about to read the poem, he commented to his audience, "You have to be careful of that one; it's a tricky poem -- very tricky," perhaps intending to suggest the poems ironic possibilities. A New York Times Sunday book review on Brian Hall's 2008 biography Fall of Frost states: "Whichever way they go, they're sure to miss something good on the other path."