Yesterday afternoon, while planting bulbs, my son pressed down a bit too hard on the steel bar sticking out of the side of the coring tool he was using to make holes for the bulbs. The 8mm steel bar promptly sheared off, snapping at the base. He was wearing imitation leather boots (he's a vegetarian) with no steel reinforcement. What I need to know is, are his feet harder than steel, or is it the plastic soles of his boots, and if it's the boots, how come he didn't break any toes? I think a more parsimonious explanation is that, as he pressed down on the tool, a cruise missile struck the bar at its base, shearing it off, but he and my wife failed to notice it because they weren't expecting anything like that to happen.
Or, y'know, maybe there's no absolute physical law saying that hard things can only be damaged by harder things. But that's just crazy talk.
Dave