I was told once by a physician who was, at the time, looking at my broken collarbone, that the collarbone is in fact designed to break when a certain amount of force is exerted upon it. This "break" sort of short-circuits the force of an impact on the shoulder or arm and keeps the impact from reaching your neck and/or head, causing spinal injuries or head trauma. So the fragile collarbone is actually a design feature of the human body.
Maybe the doc was dumbing it down for me, but it made sense at the time.
Doesn't expecting the unexpected make the unexpected expected?