"Walking, then, is a perpetual falling with a perpetual self-recovery. It is a most complex, violent, and perilous operation, which we divest of its extreme danger only by continual practice from a very early period in life. We find how complex it is when we attempt to analyze it, and we see that we never understood it thoroughly until the time of the instantaneous photograph. We learn how violent it is, when we walk against a post or a door in the dark. We discover how dangerous it is, when we slip or trip and come down, perhaps breaking or dislocating our limbs, or overlook the last flight of stairs, and discover with what headlong violence we have been hurling ourselves forward."
- Oliver Wendell Holmes, "The Physiology of Walking," from Pages From an Old Volume of Life: A Collection of Essays, 1857-1881. Seventh Edition. Boston: Houghton, Mifflin and Company, 1887