The loan shark's. Duh. That doesn't relate at all to the previous scenario, where no force or.violence was employed.

Contract law is contract law. It's built on the express premise that a promise, once made, ought to be honored, and that refusal to honor a promise absent very good cause is grounds for restitution.

You could replace fiat currency with gold notes and the case is still the same. Unless someone is threatening or coercing you into an agreement, you've volunteered into it. The responsibility is on you.