The poet would sigh because he realizes the significance of the choices he has made in his life, particularly when it comes to the road not taken. In Robert Frost's poem "The Road Not Taken," the poet reflects on the choices he has made and the paths he has taken in life.

The Significance of the Poet's Sigh:
When the poet sighs, it signifies his contemplation and reflection on the roads he did not choose to take. It indicates a sense of regret or longing for what could have been.

Exploring the Poem "The Road Not Taken":
- The poem begins with the poet coming across a fork in the road, where he must make a choice.
- Frost uses the metaphor of the two roads to represent the different paths or choices we face in life.
- The poet acknowledges that he cannot take both paths and must make a decision, which leads to his sigh.
- The sigh represents the weight of the decision and the awareness that choosing one path means sacrificing the other.
- The poet then reflects on the road he ultimately chose, describing it as less traveled, suggesting that he took the unconventional path.
- However, he also recognizes that both paths are equally appealing and that he will never know what would have happened if he had taken the other road.
- The final lines of the poem reveal the poet's anticipation of telling the story of his choice in the future. He suggests that he will claim that taking the road less traveled made all the difference, even though he knows deep down that both paths were equally valid.

In Conclusion:
The poet sighs in "The Road Not Taken" because he understands the significance of the choices he has made. He contemplates the road he did not choose and acknowledges the potential outcomes it could have brought. The poem serves as a reminder to consider the paths we take in life and to reflect upon the choices we make.