The traveler in "The Road Not Taken" reflects that taking "the road less traveled by" has made "all the difference". This could be taken to mean that the road he chose brought him success; that choosing a route that was somewhat less popular led him to success in his own life. However, the phrase "And that has made all the difference" doesn't necessarily indicate that he has been successful or otherwise in his life; it indicates that his choice of roads affected all of his future. The place he is at in his life as he reflects can be traced back to the choice between two routes.
If he is indeed successful, though, it would seem to be because he determined to make a choice and then stuck with it. He was equally attracted to both roads, both seemed "just as fair", and it was with regret that he could not follow both that he finally made a choice and took the "road less traveled by". He would like to think that another time he could explore the other road, but he realistically knows that will not happen, "knowing how way leads to way". He could have vacillated between the two roads indefinitely, never fully committing to one or the other, and therefore never getting anywhere. Success, we can understand from this, lies in making a choice, committing to it, and following and accepting where it leads.
Choosing the path "less travelled by" is the key to success in Frost's poem, which inturn he refers to the less chosen profession of writing which has made all difference in his life and career.
Perhaps taking "the road less traveled by" is the key to success.