system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 how wet paper is so weak but if left to dry it returns to the same(or close) to the same strength.

What is the water doing that severely weakens the structure but if allowed to dry it seems to return to the same strength, or at least really close to the same strength as before.
gpt
Paper is made from cellulose which forms long interconnected chains and fibers. These chains and fibers are held together by a special type of bond called hydrogen bonds. Hydrogen bonds are quite strong and provide a lot of the structural properties you see in paper. 

Water is also capabale of hydrogen bonding. When water impregnantes the fibers, it interupts the hydrogen bonded cellulose-ceullose network, to create new cellulose-water hydrogen bonds. As a result, the fibers become disentangled and separated. This is why paper is so much weaker when it is wet. 

If the paper is allowed to dry, those cellulose-cellulose hydrogen bonds are allowed to reform, and the paper  (mostly) regains its mechanical properties.