system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does putting a slice of bread in a bag of cookies make the cookies softer?

So I baked cookies on Thanksgiving and a friend I invited over who doesn't have family out here told me to put them in a bag when putting them away but include a slice of bread. 

Now putting the cookies in a bag is nothing new to me, but the bread part sorta made it seem weird. When the cookies came out of the oven and cooled they were sorta hard on the bottom. Not rock hard, but not gooey. After Thanksgiving dinner I put them in a bag and threw in a slice of bread. Come today, I eat a cookie and it's the softest cookie I've ever had, and the hardness from before was gone. 

Why and how does this happen?
gpt
Cookies contain a good deal of moisture in them, more than the air does usually, and because nature likes things balanced the moisture in the cookies leaves, to balance things out. 

Bread, a lot like cookies, has a lot of moisture and, when compared to cookies, "gives up" that moisture quicker. This means the bread dries out before the cookies!