"The Road Not Taken" centers on the concept of choice. The path that the speaker is walking on is splitting in two directions, and he has to decide which way to go. This path is not just in the woods, but also represents a decision in his life. Something in his life is changing, forcing him to make a choice. Yet he has a really hard time deciding – one moment, he thinks one way is better, the next, both paths are about the same. Whether or not he has a reason why the choice he makes is better, he has to make it. And that choice changes his life.
Despite what the speaker's memory tells him later, the roads in this poem are equally traveled, making the speaker's choice more difficult.
The speaker is purposefully ambiguous about whether or not he's happy with his choice.