In the poem "The Road Not Taken" by Robert Frost, the roads symbolize choice, while the "yellow wood" could refer to a concept like "life." According to this interpretation, the poet is therefore suggesting that life often contains a choice of paths to take.
These choices often create points of no return for the person making them, as indicated by the speaker's words in Stanza 3, indicating that he would probably not return to try the other road.
The idea that both roads (or choices) appeared both viable and appealing is juxtaposed with the poet being one person. He cannot take both roads at the same time. Also, having made his choice, this would inevitably lead to further choices, creating new roads and new choices.
The final stanza then symbolically explicates the core idea to the reader: The road that is not taken or the "road less traveled" is the one that is most likely to lead to more adventure and potentially more fulfillment in life. The poet suggest that the less conventional choices in life are therefore the ones to make as much and as often as possible, because it makes "all the difference." (Line 20)