And looked down one as far as I could
To where it bent in the undergrowth.
Then took the other, as just as fair,
And having perhaps the better claim
Because it was grassy and wanted wear;
Though as for that the passing there
Had worn them really about the same,
And both that morning equally lay
In leaves no step had trodden black.
Oh, I kept the first for another day!
Yet knowing how way leads on to way,
I doubted if I should ever come back.
I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I--
I took the one less traveled by,
And that has made all the difference.
As he accepts that this choice may ultimately define his life, he expects to feel a little melancholy about his decision. He is not completely confident and expects to feel some regrets that he didn’t go the other way. The tone here is gently comic or mock-melodramatic, but there’s a serious wistfulness behind it . 
 
 The sigh can be one of regret or satisfaction. Similarly, the difference that he talks about can be one that is welcome, or otherwise.
The Road Not Taken