Many of you know the game of paper, scissors, rock. Two players hold their hands behind their back and on the count of three put out a flat hand, two fingers extended, or a fist, representing paper, scissors, or rock. Assuming the players display a different hand, the player displaying the "stronger" hand gets to whack the other player's hand. The circular hierarchy is paper covers rock, scissors cut paper, and rock breaks scissors.
This hierarchy doesn't always hold. The most obvious is that rock can hold down paper. How about that paper wears down scissors? You can see it when your scissors need sharpening after years of cutting paper. Or a razor blade gets dull cutting whiskers.
I saw it big another way last week. I checked the blade on our chipper. It had many knocks in its edge, including a one-sixteenth chip. All that has gone through the chipper is wood, no stones or other hard debris. Paper is made from wood. That wood, all from softwood trees, wore out a high-quality steel blade. All in probably less than 20 hours of use.
