The stamp that changed the post

Before 1840, British letters were paid for by the person who received them, and the price depended on distance and the number of sheets. A letter from Scotland to London could cost a labourer a day's wages.

The system had consequences that look absurd now. Recipients refused letters they could not afford, so postal workers carried mail that produced no revenue. Senders wrote in tiny script and crossed their lines at right angles to fit more on one sheet. Some developed codes in the address itself, so that the recipient could read the message from the outside and then refuse delivery, paying nothing.

The reform was proposed by a teacher, not a postal official, and it was radical in a way that was hard to argue with. One low price regardless of distance, paid in advance by the sender, proved by a small adhesive label. Opponents predicted ruin: without distance pricing the long letters would be subsidised by the short ones, and revenue would collapse.

Revenue did fall at first. Volume rose so steeply that it recovered within a decade, and the reason was the part nobody had modelled. A great deal of correspondence had never been written at all, because the writer knew the recipient could not pay. Removing the uncertainty did not simply shift existing letters to a new price; it created letters that had not existed.

This is the pattern that makes demand hard to forecast. A price can suppress not only purchases but the entire habit of purchasing, and the habit returns more slowly and more completely than any model expects.