There is a concept in physics called angle of repose. Set an object, a book say, on a plank. Now slowly tip up one end of the plank until the moment when the book just starts to slide. The angle between the plank and the horizontal is the angle of repose, where the component of the gravitational force down the plank becomes greater than the maximum friction force holding the book at rest.
Or, in more evocative terms -- As I write I am lying on the couch with the laptop in my lap, in perfect repose. If you started tipping up the couch, at some point I'd go sliding into a heap at the bottom. That's the angle of repose, or perhaps it would be more accurate to call it the angle of the end of repose.
This comes to mind because I just spent fifteen minutes on my knees in the yard watching ants excavate a nest in the ground. One by one they scurry out of the hole carrying a tiny grain of sand, which they dump in a ring around the hole. A circular pile. Now if the ants just dumped their burdens at the mouth of the hole, pretty soon the pile would get so steep that the sand grains would slide back into the hole. Instead, the circular ring gets higher and wider, with a slope that never exceeds the angle at which the grains will slip -- the angle of repose.
Now here's the thing: the ants almost invariably carry their grain to just beyond the top of the pile. If the grain slips, it will slide away from the hole. These tiny ants, hardly bigger than sand grains themselves, understand a little physics in their mysterious instinctive way.
Wallace Stegner has a novel titled "Angle of Repose." It is indeed an evocative phrase. In a job, in a relationship, in life itself, many of us instinctively seek that maximum degree of individual gratification that will satisfy emotional needs without doing violence to our essential repose, and that of those around us -- the art of walking close to the edge, the thrill without the spill. Every day in the news we hear of folks -- politicians or celebrities -- who tipped the plank too far, whose lives went sliding into self-destruction, who failed to grasp, metaphorically speaking, something that a tiny ant instinctively understands.