In the early 1900s, Franz Kappus was an aspiring poet enrolled in military school when he wrote to Rainer Maria Rilke for writing advice. Rilke’s response turned into a six year correspondence, and spawned Letters to a Young Poet:
“ . . . ask yourself in the most silent hour of your night: must I write? Dig into yourself for a deep answer. And if this answer rings out in assent, if you meet this solemn question with a strong, simple “I must”, then build your life in accordance with this necessity; your whole life, even into its humblest and most indifferent hour, must become a sign and witness to this impulse.”
Austin Kleon, the inspired artist-poet, cleverly illustrates Rilke's writing advice. See more here.