Wallas also quotes the German physicist Hermann von Helmholtz, who described how new ideas would bubble up after he’d worked hard on a problem and hit a wall: “Happy ideas come unexpectedly, without effort, like an inspiration,” he wrote. “So far as I am concerned, they have never come to me when my mind was fatigued, or when I was at my working table … they came particularly readily during the slow ascent of wooded hills on a sunny day.”
