Are you seeking "tender is the night," a phrase used by F. Scott Fitzgerald as the title of his 1934 work about an American psychologist Dick Diver and his wife Nicole, who is psychologically disturbed? Set in southern France with a cast of characters much like the real friends of the Fitzgerald's--wealthy, idle, sophisticated and dysfunctional-- the novel has autobiographical overtones as Zelda Fitzgerald herself was mentally unstable.
I think you will derive a better answer with a bit more clarification. The poem itself is loaded with powerful lines. I have included a couple and encourage you to revisit these lines in the context of the poem to gain a greater and much deeper appreciation for Keats' words and employment of language:
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, 25 Where youth grows pale, and spectre-thin, and dies; Where but to think is to be full of sorrow And leaden-eyed despairs;
Away! away! for I will fly to thee, Not charioted by Bacchus and his pards, But on the viewless wings of Poesy,
Already with thee! tender is the night, 35 And haply the Queen-Moon is on her throne,
The "tender is the night" quote is a fairly powerful one.