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.
If there is no one in sight in FRONT of you, and a line of assorted vehicles BEHIND you, it is NOT because they always wanted to be in a parade. — Florida Lime.