And much like weight gain, the propensity for buying things varies from person to person.

Some don't need much, others will always or almost always spend more than they have, but traditional financial advice will be the same for both groups.

This is real. I approach these conversations based on if the person would be open to learning the same way I avoid religious and political discussions.

It is a deeply emotional response from most people, they know what they are doing is stupid. They almost never need me to tell them.

My mom was an accountant and she looked flabbergasted when I told her her $2k/month timeshare was costing her $24k/year, sucking up almost all of her social security.

Does this not point to more of a psychological issue such as avoidance, not a financial illiteracy one?

I don't want to come off as aggressive because this is your family, but I'm guessing your mother can multiply 2 by 12.

I'm not at all disparaging accountants here but I don't see any reason why they would have superior budgeting capabilities. Accountants are generally in charge of recording the accounts and not actually setting and spending the budget no?

The person I would be shocked to be bad at this would be someone like the owner of a boring and non-expanding local business, like a tire repair shop.

I agree with this. Most people that abuse credit card debt know the ins and outs of every bylaw on credit cards, they just… need the money and don’t care about their credit rating.

Yep, most people are hyperbolic discounters. Cash Today is worth 10x more than Cash even from a month now. So, 20% APR doesn't faze them