" I discovered what a mental stimulant physical labor could be; not mere physical labor, I should add, but absolutely spine-bending, lung-racking, gut-ripping, ligament-tearing, and ball-breaking physical labor. But as long as the task is both onerous and repetitive, I discovered, the mind is not only free to wander to more imaginative climes, it actually flees to higher planes. "

― Dan Simmons , Hyperion (Hyperion Cantos, #1)