At the beginning of the poem, the speaker finds himself at a point of decision - which road should he take? Deeper than the obvious choice of which way to travel, this reflects an individual in the autumn of life trying to determine a direction for the remainder of that life; to follow the commonly traveled path or "the one less traveled by."
The speaker recognizes that either path has merit. There is some desire to be able to travel both paths, but the speaker realizes only one path can be traveled at a time and that s/he probably would not be able to revisit this place in the road (or in life) and choose to take the path not chosen in the poem.
Eventually, the decision is made to follow the path that has not been used as frequently. The speaker understands that this decision will make "all the difference" in the remainder of his/her travels, and his/her life. There is some regret ("telling with a sigh") at not being able to experience the other alternative, but I interpret the poem as reflecting acceptance of the decision that was made.