"The Road Not Taken" is often misunderstood as meaning that the speaker believes he took the "road less travelled by." Some have interpreted this to mean an allegory: taking the less travelled road leads to a different and perhaps more rewarding experience. I do favor the reader response theory which states that the reader, not the author, has the freedom and responsibility to interpret a poem, novel, etc. in any way he/she sees fit. However, I think this analysis is a misreading.
This "take the harder road" analysis really misses the meaning of the poem. Note that earlier in the poem, the speaker says that the two roads were worn "about the same." When he came to this decision, both paths looked similar. It would be incorrect to say that he chose (or believed that he chose) the "less travelled" road because they looked equally travelled.
This poem is not about triumph from having chosen the more difficult road. It is about the uncertainty we sometimes have in making decisions and how it is sometimes impossible to know which path will be the most rewarding. In the same respect, this poem is about the "what ifs" of life. What if he had taken the other (seemingly identical) road? He can only guess. He also concludes with a "sigh." Knowing how "way leads on to way," the speaker knows that he probably can't go back and choose the other path. (For an obvious example, at 50 years old, you can't go back and take the other job at 25. But this could be about a trivial or monumental decision.) The sigh might indicate regret, second guessing, or even just a playful imagining of what his life would have been like had he chosen the other road.