The old key kept in a drawer can hold an address that no longer needs you.

Keys outlast the doors they belonged to. Somewhere in a drawer is one for a flat where other people now cook and argue and sleep, a place that carried on perfectly well after you left. Keeping it is not foolish; it is a small physical proof that you lived somewhere, even though the somewhere has no further use for you.

Take it out and decide what it is for. Some keys are worth keeping as objects and some are just weight, and the difference is whether the memory arrives when you hold it. There is no obligation either way this week.