system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If my kitchen knife (made of steel) is harder then my cutting board (made of wood) and is harder then the foods I cut (fruits, meats, vegetables), why would I ever need to sharpen the knife?
gpt
Generally when your knife becomes blunt it's not because the metal has been worn away but because the fine edge has been bent over. This is why running a steel along the edge brings it back to sharpness - it's not removing metal, it's pushing the bent bit back into alignment.

So - since you can bend metal with your fingers, it's not surprising that food can bend the very fine edge of your knife.

Even if this weren't the case, hardness isn't a winner-takes-all thing. A soft material can, in time, wear down a hard one.