Marlow, from Heart of Darkness by Joseph Conrad, is not a typical seaman and has a philosophical edge to him which is what allows this journey to become so much more than a physical trip. Kurtz is a man like no other who has a deep impact on everyone he meets but others are powerless in his presence. "He came to them with thunder and lightning, you know...and very terrible." Even when there is opportunity to leave, his followers, "pilgrims," remain loyal. Marlow begins, during his journey into the depths of Africa, to recognize something in himself which had escaped him before. The physical and very arduous journey allows him to delve into his own thoughts and the choices, unconscious or otherwise, that he has made. Some of his choices create similarities between two conspicuously different people:
I found myself lumped along with Kurtz as a partisan of methods for which the time was not ripe: I was unsound! Ah! but it was something to have at least a choice of nightmares.
Robert Frost in his poem The Road Not Taken, also allows the reader to take a figurative rather than a strictly literal, look at choices. Originally written for his friend who found even the simplest decisions difficult to make, the reader is left contemplating "the difference" his choices have made. Marlow's choices have certainly left their mark on him.
Marlow, the narrator of Heart of Darkness and something of an observer in his own journey into Africa, separates himself from the reality of the situation. Having chosen to make this journey and gone to a lot of trouble to ensure he could attend to Kurtz, he recognizes how choosing to do this would not have been a popular choice for most but, for him, a necessary one, even to the point that it- "the choice-" has been "forced upon me." Marlow knows that he could have made other choices that would not have exposed him to such trauma. The unpredictability of the journey also adds to the fact that it is "the road less traveled;" one where there are unexpected events and even feelings. There may be many others who have or will travel the same route but many of them will not have the same enlightenment as Marlow because, to them, there is no significance. This is just another voyage.
The facts about Kurtz would have remained unknown had Marlow not recalled this story. Choosing Kurtz as his "nightmare" acknowledges that Marlow has in fact some control over his choices and he is able to "awake" from this one, hopefully a better person.
I am not sure there is a parallel. In Robert Frost's poem, the narrator seems to imply that his life has been somehow enriched by choosing a less-traveled path. I would suggest that Marlow's association with Kurtz did not have a positive influence oin his life.
Also, a path less traveled by implies that it was a choice, and I don't believe that Marlow had much choice in the matter.
It also implies that the same or similar choice might have been made by others, or could be made by the reader at some point in the future. The poem's narrator would seem to advocate for some people to make the less common choice.