I think that this poem is about regret, not the regret of the choice made, but that of not being able to choose both paths. In the first two lines of the poem, the speaker is at a fork in the road of and knows that he can only go down one of these roads. The word “yellow” in the first line makes me think of flowers, nature, and ultimately life. This is the path of life, which is full of choices.
In the second and third lines, the speaker regrets not being able to go down both roads at the same time as the same person. If he went down one road and then had the opportunity to go down the other road, it would be different because he has changed by going down the first road.
In the fourth and fifth lines, the speaker tries to see what the outcome of going down one of the roads would be, but it is too long and bends into the undergrowth. The speaker can only see so far without actually making the choice to go down that road.
In the sixth and seventh lines, the speaker looks at the other road and admits that it is just as good as the first road, but maybe better. It may look better, but he can’t really tell which road is better or worse just by looking at them.
In lines eight through ten, he reveals that this second road appears to have been traveled less, but not very much because both roads are worn about the same.
In the eleventh and twelfth lines, the speaker says that no one has walked either of these roads this morning so he can’t just follow someone along one of the paths or even take the other path to be different. He has no guidance in making his choice.
In line thirteen, he finally decides to take the second, less traveled path. In lines fourteen and fifteen, the speaker realizes that after going down this path he is going to get caught up in other things and will probably never again have the opportunity to go down the other road. If he later finds out that going down this road was a big mistake, he can’t go back...