I am writing about literacy, numeracy and the gap between those and financial literacy, but can't think of a single word for the latter. Specifically the gap experienced by someone who can read a bank contract, and verify that the maths is correct, but can't see that they have no ability to meet the terms, or no margin for error (viz, they might be able to make payments now, but if another cost arises they won't be able to meet both). Not an optimist, but someone who looks at a budget where the critical line is "Available funds per week: $100. Repayment per week: $101" and says quite sincerely "yes, I can do that". Or possibly more likely, someone who never thinks to actually make the budget and just says "I earn $500/week, $101/week for the loan will be fine".
The second group are people who, while literate and numerate, are not ....
The .... are not necessarily naive, but nonetheless find themselves in unsustainable debt by means they don't understand.
I need to distinguish those people from people who have no choice but to knowingly sign an impossible contract in order to delay the inevitable. So someone who, for example, needs their car to keep their job but can only borrow to repair it on impossible terms (payday loans, for example). They know they're in trouble, but all they can do is defer the problem and hope for the best.