The lightly satiric tone of Frost's line "I shall be telling this with a sigh" in "The Road Not Taken" suggests the theme of indecisiveness. That is, the reluctance of someone to make decisions lest the person make the wrong ones. Of course, the ultimate problem is that the ambiguity and lack of decision sometimes leads to more negative results than anything else.
In order to indicate this thematic indecision, Frost employs certain literary techniques:
In the first stanza, the word And is repeated at the front of each line, indicating hesitation; for, the use of the same word "And" holds back the forward movement.
In the second stanza, the word as is repeated twice in the first line, and then in the fourth line in such a manner that it pulls back the phrases following this word:
Then took the other, as just as fair,...
Because it was grassy and wanted [here "wanted" means "lacked"] wear;
Though as for that the passing there
The word "same" and its idea in "just as fair" is repeated in this second stanza, as well.
In the second stanza there is no forward movement of thought as the speaker deliberates on the paths circling in thought with such words as "perhaps," "because," "though," and "really about the same."
Such words as "knowing how way leads on to way," "doubted," and "if ever I should" are used in the third stanza.
While most of the poem is written in iambs [unstressed syllable followed by a stressed syllable (ta DUM), which is the normal pattern of spoken English, there is a slowing in each line with the insertion of an anapest [unstressed syllable, then another unstressed, followed by a stressed]. This slowing is suggestive of delay, hesitation, and indecision.
For Robert Frost trees serve as borders. His first line reads that there is "a yellow wood." The addition of the word "yellow" which often connotes danger and being overly analytical and the woods and later "undergrowth" suggest lack of movement, something that accompanies indecision.
In the third stanza, Frost writes that two paths "diverged in a woods," suggesting again the border and end of movement. Also, in the third stanza, the color black appears. This use of the black can symbolize negative conditions, too.