Imagine this: you live in a society where being unable to pay back a loan is punishable by death. (Why, you ask? Because I'm the emperor of this society, and I make the rules, and those are the rules.)
Now imagine that you were born very poor, through no fault or choice of your own. And society is structured in a way which entails that, through the normal course of life, you've come to owe me $100 dollars... which you couldn’t avoid, and you simply cannot pay back, now or ever.