A household accumulates two different kinds of asset over a lifetime, and only notices one of them. The first is the things themselves: the accounts, the policies, the deeds, the documents in the drawer. The second is the knowledge of where all of that is — the index, held almost always in one person's memory, written down almost never.
The second asset is worth more than it looks, because the first is inaccessible without it. And it is the one guaranteed to be destroyed by the event the whole arrangement was built for.
Two different failures
Consider losing the safe. A fireproof box is destroyed, or a solicitor's firm is absorbed and the files move, or a document is genuinely mislaid. This is recoverable, usually tediously. You know what was in it. You know who issued each item. Institutions reissue documents to the people entitled to them. The estate is delayed and somebody is annoyed, but the position is retrievable, because you still hold the index.
Now consider losing the map. The documents are all intact, filed sensibly, in a location nobody has been told about. Nothing has been destroyed. Nothing needs reissuing. And the estate is administered without them, because the executor cannot search a house indefinitely, and at some point they must proceed with what they can prove.
The second failure is worse, more common, and almost entirely unmitigated in ordinary households.
Why the map never gets written
Because writing it feels like the least valuable task available. Organising the documents produces a visible result: a tidy folder, a labelled box, a sense of completion. Writing down where the folder is produces a single sheet of paper that appears to say nothing the household does not already know.
It says nothing the household knows while the household includes the person who filed everything. The sheet is not written for today. It is written for the specific afternoon when the person who knows is not available to be asked, and it is the only artefact in the entire arrangement designed for that afternoon.
What a usable map contains
Not the contents. The map is not a copy of the estate and should not try to be — a document that reproduces account balances is out of date within the month and creates a security exposure for no benefit.
A usable map records categories and locations. That a will exists, who drafted it, where the original is held. Which institutions hold accounts, without the balances. That there is a policy, with the insurer and the reference. Where the deeds are. Who the adviser is. Which drawer, which cupboard, which firm, which address. It is a document of pointers, and pointers age far more slowly than values.
It should also record the things that exist only as knowledge: that the shed roof is under a guarantee, that the boiler service is prepaid, that one account is dormant but deliberately open. These never appear in institutional records anywhere, and they disappear completely.
The index is the only part of a household's records that cannot be reconstructed from outside the household.
Keeping the map current
A map has one maintenance property worth understanding: it decays more slowly than the things it points at. Balances change monthly. Locations change every several years. Institutions change more slowly still. This is why a pointer document remains useful long after a valuation document has become misleading, and why the annual review of a map is a short task rather than a rebuild.
The practical rule is to update the map when something moves, not when something changes value. New account, new entry. House move, revise. Solicitor changes firm, amend one line. It is a few minutes a year, spent on the only document in the house that your family cannot do without and cannot obtain anywhere else.