Frost could not have known what a stunning effect his repetition of the last line [in "Stopping by Woods on a Snowy Evening"] was going to produce. He could not even know he was going to repeat the line. He simply found himself up against a difficulty he almost certainly had not foreseen and he had to improvise to meet it….

It must have been in some such quandary that the final repetition suggested itself—a suggestion born of the very difficulties the poet had let himself in for. So there is that point beyond mere ease in handling a hard thing, the point at which the very difficulty offers the poet the opportunity to do better than he knew he could. What, aside from having that happen to oneself, could be more self-delighting than to participate in its happening by one's reader-identification with the poem?…

[The] human-insight...