When people think about what is exposed, they think of facts: an address, a value, a relationship, an event. They think less about the small, dull pieces of information that do the connecting, and yet those are often what matter most.

An email address, a telephone number, a username, a handle chosen long ago: each of these seems trivial. None of them is sensitive in the way a home address is. But each has a particular property. It tends to be used in more than one place, and so it links those places together.

A single email address may have been used to register a dozen services over the years. Anyone who finds it on one of them has, in effect, a key to the others. A telephone number given to several institutions ties their records of a person into a set. A username chosen once and reused, as people naturally do, connects an account in one corner of the internet to an account in another that the person would never have thought to associate.

This is why such identifiers matter out of all proportion to how interesting they appear. They are the connective tissue. The work of assembling a picture of a person is largely the work of linking separate records, and a reused identifier does that linking automatically. A person who guards every individual fact but uses the same handful of identifiers everywhere has, without realising it, made the assembling easy.

The lesson is not to live without an email address or a telephone, which is no lesson at all. It is to recognise that these quiet identifiers are doing connective work constantly, and that they belong in any honest account of exposure. Often the most useful single step in reducing how easily a person can be assembled is not the removal of some dramatic fact, but attention to the small, repeated keys that tie everything else together.