system
Given the following post, respond as if you're commenting on Reddit:
human
Why doesn't glue dry in the bottle?
gpt
Most contain a solvent that is supposed to evaporate away as the glue dries and hardens.  A good bottle that can be closed properly will keep the evaporation during storage to a minimum.  Certain epoxy glues, on the other hand, works by undergoing a chemical polymerization reaction when two different materials are mixed together.  As long as the two ingredients involved are kept separate and prevented from reacting, they don't become sticky/hard.