system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If I throw my dress shirt on the floor overnight, it wrinkles. Why then if I hang it up the next day, doesn't it unwrinkle?
gpt
When you throw it on the floor, you've just taken it off. The fabric has absorbed a lot of humidity from your body, and is warm, both of which make the cotton more likely to hold a new shape as it dries and cools.

This is why ironing works - the heat and damp soften cotton slightly allowing it to set into a new (hopefully flat) shape.