A duplicate key is trust prepared for a day when ordinary timing fails.

Handing over a spare is a bet on a future you cannot specify. It is not a plan for anything in particular, just an acknowledgement that at some point you will be locked out, or ill, or away when something floods. Trust of this kind is practical rather than sentimental, measured in what you are willing to let someone see unannounced. Very few people are given one, and most of us could not say exactly why those ones.

Think about who holds yours and whether the list still matches your life. Adding a name, or asking someone to hold yours, deepens a friendship more plainly than most conversations do.