Garbage Collection:

A computer science analogy referring to that thing that happens in real life where, at unpredictable intervals, someone comes into your house, tells you to stop whatever you're doing, and rummages through your belongings to see which ones you're not using.  Some of that stuff they'll take away; the rest, they'll leave there just in case, because they're not totally 100% sure whether you're finished with it or not.  At last, with the inventory finished, you can now go back to what you were doing.

You no longer remember why you hired them to do this and why you can't just throw garbage in the garbage can when you're done like a normal person.