system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Can a material only be scratched by a harder material?

My father used to say only diamonds can scratch other diamonds.  Like, he would say that it's OK to play with a puzzle on a walnut table because the wood is so much harder than the paperboard, but it wouldn't be OK to play that finger knife game from Alien.  And it makes sense to me on some level.

But if I hack at a tree with an axe for a while it will definitely get dull.

Does what my father used to tell me hold any water?
gpt
Your Father is correct. Things can only be scratched by things of equal or higher 'hardness'. The axe you use does get dull for several reasons. Firstly the thin edge does get bend and mushed out of shape by the impact of the axe's weight. Then for moments there is a really high friction that heats things up. And then even in wood there are minerals that can act abbrasive to metal.

Just cause you cannot scratch a diamond with a metal hammer doesn't mean you cannot smash it to dust with the weight of a metal hammer.