Different types of glues.
Some glues harden and simply bind.
Some glues stick to a surface.
Some glues chemically alter the surface and bind to it.
Se glues melt things and fuse them together.
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By altering the composition or chemicals in the glue, you can make it more or less sticky. More or less flexible, or brittle and breakable.
So many different types. A terrible glue is just an incorrect choice.
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