system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do soft baked goods go hard when they get stale, and hard baked goods go soft when they're stale?
gpt
Harder baked goods absorb moisture over time because they start out dry compared to the moisture in the air and become softer as a result.

Softer baked goods that already have moisture in them which is used chemically to make their gel-like structure instead lose moisture over time (since there's less moisture in the air than in them).  This makes them harder.