In 1903 Allen published his third and most famous book As a Man Thinketh. Loosely based on the Biblical passage of Proverbs 23:7, "As a man thinketh in his heart, so is he," the small work eventually became read around the world and brought Allen posthumous fame as one of the pioneering figures of modern inspirational thought. The book's minor audience allowed Allen to quit his secretarial work and pursue his writing and editing career.