"The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money. Take boots, for example. ... 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. ... 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 socio-economic unfairness."
- Terry Pratchett, Men at Arms
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Dollar stores, even when they're actually giving you low prices (and not just charging $1 for 1 of something that you could get a 3-pack of for $2 elsewhere), are often selling lower-quality versions of the products they sell—sometimes versions specifically made for them, but without any visible difference in packaging.