"Ode to a Nightingale" (lines 21-30)

I'll admit that I've never been a big fan of Keats, but some lines strike me as eerily unforgettable. Among these, the third stanza of "Ode to a Nightingale" has to rank near the top. In the first two stanzas, the speaker of the poem describes his world-weary heartache and then contemplates drinking too much wine so that he "might...leave the world unseen" and, with the nightingale, "fade away into the forest dim" (19-20). The third stanza explains just what it is that the speaker seeks to escape—he wishes to...

Fade far away, dissolve, and quite forget
  What thou among the leaves hast never known,
The weariness, the fever, and the fret
  Here, where men sit and hear each other groan;
Where palsy shakes a few, sad, last grey hairs,
  Where youth grows pale, and spectre-thin, and dies;
    Where but to think is to be full of sorrow
      And leaden-eyed despairs;
  Where beauty cannot keep her lustrous eyes,
    Or new Love pine at them beyond to-morrow.

I don't know of a more poignant expression of human sorrow anywhere in English literature. The speaker wants to escape from "The weariness, the fever, and the fret" of humankind, "where men sit and hear each other groan." It's a bleak picture, and one might wonder just what in the human experience could evoke such despair. Well, initially it appears to be a familiar comment on mortality and the sheer indignity of age, "Where palsy shakes a few, sad, last grey hairs." But such infirmities are not limited to the aged, for youth too "grows pale, and spectre-thin, and dies." This line often gets an editorial footnote drawing the reader's attention to the fact that Keats had recently lost his brother to "consumption" (tuberculosis), and no doubt this fresh tragedy was weighing heavily on Keats in early 1819. But to read the line in this way also, in my view, limits the significance—while Keats may have his brother's death in mind, that death is the example of a larger point about mortality and the fragility of even youthful life and vigor. Death, pain, and frailty are not restricted only to the aged and the palsy-stricken. Youth, beauty's "lustrous eyes," and even Love itself are short-lived experiences. Though we may wish to merge into some realm of transcendant and immortal beauty as that represented here by the nightingale's song, we are only too soon pulled back into a gnawing sense of pain, sorrow, and loss. It's little wonder that "to think is to be full of sorrow / And leaden-eyed despairs."