I agree with you but there is also the dynamic that there is always other richer people than you with richer lifestyles. So while you might think that one jet is enough for you if you had friends who didn't own a jet. When all your friends own 3 jets it makes you feel like you should also own 3 or whatever random expense you can imagine.

And while you say "human nature" I'd rather say it's "human illness." They someone are within a strata of society where there is no limit, a 20 minute private jet flight or a $20,000 meal is not out of the question and is in fact the norm.

They buy a fully renovated house for $10 million but then gut it to renovate it to "their tastes" and then live in it for two weeks of the year. There's just not culture to tell them it's excessive.