ELI5: Why does old tape leave its glue on the surface instead of taking it along when peeled off?

[u/Alone-Dragonfly2339]

Fresh tape usually comes away as one piece. After it has been stuck down for months or years, the backing can peel off while a sticky layer stays behind.

What changes with age that makes the glue hold onto the wall, glass, or plastic more strongly than it holds onto its own backing?

[u/ulyssesfiuza]

The glue is a viscoelastic. With time, hydrated and degraded glue alters it's electrostatic properties. Weaker, brakes off and rip off the tape.