A useful way to think about exposure is in terms of cost. For any given fact about a person, there is an effort required to obtain it: a price, paid in time, money, skill, or access. The landscape of a person's privacy is shaped, more than by anything else, by that schedule of prices, and the most important thing to understand about it is that the prices have fallen.

Once, finding out about a person was expensive across the board. Records were dispersed and hard to reach. Searching them took specialist knowledge. Joining one to another was laborious. The cost of assembling an account of a person was high enough that it was only done when there was a strong reason, and a budget, to do it. Expense was, in effect, a form of privacy. It kept casual enquiry out.

That protection has largely eroded. Records have been gathered, indexed, and made searchable. The work of joining them has been automated. An industry has grown up whose business is to lower exactly these costs and to sell the result. The effect is that a great deal of what was once expensive to learn is now cheap, and some of it is close to free.

When the cost of an action falls, the action is taken more often, and by more people. Enquiry that was once reserved for cases that justified real expenditure is now within reach of the merely curious, the opportunistic, the routine. The question has shifted from who would go to the trouble to who would not, simply because there is so much less trouble involved.

Not everything has become cheap. Some facts remain genuinely expensive to obtain, and some require access that money alone does not buy. A clear picture of one's exposure is, in part, a clear picture of this schedule of prices: what about oneself is now cheap to learn, what is moderately costly, and what is still genuinely hard.

For a person of any standing, the practical use of this idea is to assess exposure honestly in cost terms. The facts that are cheap to obtain should be assumed to be obtainable, because cheap things are obtained. Effort should be concentrated where it changes the price: on the facts that can be moved from cheap to costly, and on understanding that, as the general cost of enquiry continues to fall, this is an assessment that has to be made more than once.