system
Given the following post, respond as if you're commenting on Reddit:
human
Why doesn't glue harden while in the bottle?
gpt
Type of glue here is essential for the explanation;  but I'll take a few examples.  

1.  Superglue;  cyanoacrylic,  actually initiates bond with water molecules.  So being in an air-tight container extends the life significantly.  So without the water molecules to bond to the glue won't react and create the bond.  (This is why the stuff sticks to fingers so fast.

2.  Wood glue, elmers glue, and the like use PVA. -- it works by forming a chain (polymerization) when it dries.  The solution is usually water, so while in the container the un-evaporated water keeps the chain reaction from happening.  

3.  Rubber Cement -- works like the PVA, its dissolved in a solvent such as acetone.  This solvent evaporates and creates the polymerization bond.  So once again, a sealed container keeps it from evaporating.