Bread going stale is one of life's most personally offensive experiences. Not because of the science behind it, not because of moisture levels or improper storage, but because stale bread always seems to show up at the exact worst moment. Hungry, tired, and slightly irritable, you reach for what should be a decent slice of toast and instead get something that sounds like a crouton auditioning for a role in a soup.
The humidity argument is interesting. Store it wrong and it dries out. Store it in a bag and it goes soft and sad. There is genuinely no winning with bread. It has made up its mind about you and the relationship is clearly one sided.