After the abandonment of Hyperion, troubled by financial and personal worries, and by the dark undertones of his failing health, Keats managed a supreme effort of creative energy. There was a flurry of writing in verse, Spenserians, Shakespearian and Petrarchan sonnets, couplets, quatrains, and doggerel. Then, in the last week of April 1819, Keats's preoccupations with love, death, and poetry fused to produce the strange enigmatic power of ‘La Belle Dame sans Merci’. The poem is in a sparse ballad-like stanza form, and concentrates a wide variety of literary influences – from medieval French poetry, through the Elizabethans (especially Spenser), and right up to Coleridge's and Wordsworth's experiments in ballad metre – in a haunted expression of Keats's responses to his brother's death, his tortured love for Fanny, and his sense of being dangerously in thrall to his poetic muse. ‘La Belle Dame sans Merci’ establishes a tone of brooding and anxious incertitude, as if pervaded by Keats's dread that his conviction of poetic vocation might be fatally mistaken. It thus bears comparison with those other achievements of English Romanticism, such as Wordsworth's ‘Immortality Ode’ and Coleridge's ‘Dejection Ode’, in which the fear of poetic failure or loss of vision is ironized by articulation within a successful poem.

Before the end of the month, Keats had written the ‘Ode to Psyche’. Its themes, embracing the great paradoxes of art and life, permanence and mutability, beauty and death, are those of the major Odes that follow over the next few weeks. In formal terms the ‘Ode to Psyche’ grows out of Keats's now long-practised skill in the sonnet, as he begins the poem in an adaptation of sonnet rhymes to produce a complicated irregular form. The poem's preoccupation with the creative nurturing, gardener-like, of new growing varieties, is thus delicately shadowed in the Ode's own manifest formal genesis in a grafting of new stock on to old. The first fourteen lines do form a Petrarchan sonnet, except that Keats substitutes a trimeter line at line 12 – anticipating the use of this metrical variant in the stanzaic patterns of his more formal Odes – and he alters the last word of line 10 from the original draft reading, ‘fan’, to the unrhymed ‘roof’.