The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money.

Take boots, for example. He earned thirty-eight dollars a month plus allowances. A really good pair of leather boots cost fifty dollars. But an affordable pair of boots, which were sort of OK for a season or two and then leaked like hell when the cardboard gave out, cost about ten dollars. Those were the kind of boots Vimes always bought, and wore until the soles were so thin that he could tell where he was in Ankh-Morpork on a foggy night by the feel of the cobbles.

But the thing was that good boots lasted for years and years. A man who could afford fifty dollars had a pair of boots that’d still be keeping his feet dry in ten years time, while a poor man who could only afford cheap boots would have spent a hundred dollars on boots in the same time and would still have wet feet.

Terry made a fetish of not dating his letters. One card (saying simply “If you get this before the letter, you’ll get the letter after this. If not, not.”) was dated “no date”; the letter which begins “Well, there goes my first week as a reporter” was dated 1939; and another was dated AD 2904.

The technical term for it is infrablack. It can be seen quite easily under experimental conditions. To perform the experiment simply select a healthy brick wall with a good runup, and, lowering your head, charge. The color that flashes in bursts behind your eyes, behind the pain, just before you die, is infrablack.