The wizards from Discworld had these balls of black stuff that they were experimenting with. They seemed to fuck up the fabric of spacetime when they burst, so they were shooting them off into the distance. As they did this the world got more and more messed up, so they were having to migrate to a new place.

One of the wizards suggested that continuing to shoow the black balls around was maybe destoying the world and they should stop. The response was basically "ehhhh maybe."

By the end of the dream they bit of the world that remained was a dry, rocky, post-apocalyptic wasteland, and they were still shooting those balls around.