The Boots Theory is Captain Samuel Vimes' analogy of socioeconomic unfairness, it posits that the reason that the rich were so rich...was because they managed to spend less money. This is the situation he used to illustrate how the inability of spending extra money on certain things now will inevitably lead to spending much more in the future.

Take boots, for example. He earned $38 a month plus allowances. A really good pair of leather boots cost $50. 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 $10.

"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 $50 had a pair of boots that'd still be keeping his feet dry in 10 years' time, while the 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 is true for many other cases. Take dental health for instance, someone who was fortunate enough to have access to braces and fillings in their youth will avoid a lot of potential problems in the future. While someone who couldn’t afford braces or other forms of dental care will develop more serious and painful issues somewhere down the line, that will no doubt take thousands of dollars to fix. 

When you can afford to spend your money in a way that saves you money later, you are much better off.