In 1816, Keats met a circle of friends in London who shared his love of poetry. Among them was Leigh Hunt, the English son of American-born parents who was a crucial influence and supporter of Keats' early work, and Percy Bysshe Shelley, another young Romantic poet. Their encouragement of his poetry helped convince Keats that he could make a career as a writer.
In December 1816 he informed his guardian Richard Abbey that he was leaving medicine for good to concentrate on poetry. Abbey, who prized practical business over esoteric arts, was furious, and the two had a falling-out. Abbey never embraced his adopted son's chosen profession. When Keats gave him a copy of his first poetry collection, he responded, quite nastily, "Well, John, I have read your book, & it reminds me of the Quaker's Horse which was hard to catch, & good for nothing when he was caught - So, Your Book is hard to understand & good for nothing when it is understood."5
In March 1817 Keats published his first collection of poetry, a volume simply entitled Poems. Though readers weren't quite as dismissive as his guardian, the book did not sell well. Especially in the early stages of his career, Keats' admirers were mostly other poets, not the public. His fellow writers, many of whom had much more formal schooling than Keats, were in awe of his powers of insight, how he seemed to be able to innately sense the poetic qualities of the world around him. "The humming of the bee, the sight of a flower, the glitter of the sun, seemed to make his nature tremble!"6 said his friend, the painter Benjamin Haydon.
Like a good Romantic, Keats' powers of perception reached beyond what the senses offered in search of a deeper truth. He developed a theory that he called Negative Capability, defined as the state "when man is capable of being in uncertainties, Mysteries, doubts, without any irritable reaching after fact & reason."7 Like Samuel Taylor Coleridge's willing suspension of disbelief, negative capability was a Romantic ideal that allowed man to partake in the ineffable qualities captured only in poetry.
In the summer of 1818, Keats embarked on a six-week walking tour of England and Scotland with his friend Charles Armitage Brown. Keats went on the holiday with some reservations - his youngest brother Thomas, with whom he was very close, was ill with tuberculosis, then known as consumption. Keats was reluctant to leave him, but doctors assured him that Thomas would survive at least until his return. Keats spent the summer and fall touring, caring for Thomas and working on his first long poem, Endymion. He finished Endymion in late November. Just two weeks later, Thomas died of consumption at the age of 19.