Why do you think the poet called the poem "The Road Not Taken" and not "The Road Taken"?
Frost spends almost an equal amount of time talking about both of the roads that he discovers diverging "in a yellow wood." He describes the appeal of each, observing that "both that morning equally lay in leaves no step had trodden black."
After much consideration, however, he makes his choice and travels down "the one less traveled by." There is regret in his decision, however - an acknowledgement that he probably will not be able to return to travel on the other road, a realization that his life is being changed by the choice he has made. As he goes on with his travels, he is still questioning how things would have been different if he had used "the road not taken." He is thinking, at that point, more about the road he didn't choose than about the way he is taking.