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.

This was the Captain Samuel Vimes “Boots” theory of socioeconomic
unfairness.
	-- (Terry Pratchett, Men at Arms)