The problem is that in real life, most such cases (of buying the more expensive item) don't result in a pure savings, but rather, leave you better off in some ways and worse off in others. The cheaper shoes, IOW, will not actually be so bad that you have to replace them entirely, and you will in fact end up with with more liquid savings. The temporary discomfort and greater savings are much harder to compare to the alternative than the example suggests, so wealthier people do not always have some obvious choice that leaves them better off in every way.
So, on top of that, it's not an issue that is fixable simply by pointing this out to the poorer person and loaning them the money.