Earlier quoted context omitted.
I'll give a crack at some cliffnotes: A debt is a very natural thing for humans, because we feel compelled to provide value to people who can't pay us yet. Even before money people had gifts and favors - we give with the expectation that we'll be given something in the future - or we say 'you owe me one' when someone has helped us through an issue without sending us an invoice. So the genius of fiat currency is that…
The problem is that if everyone were to try to collect all the debts owed to them, there would not be enough currency to fulfill it all. We freely create debt, but the result is a deficit that can only be resolved by creating enough value to offset the debt. And if that is somehow infeasible, economic collapse occurs.
A pays $100 to B. B keeps $20 and pays $80 to C. C pays $80 to D. D adds $10 of his own money to pay $90 to E. Everyone's debt has been repaid, but only $110 of currency is needed for all these transactions to take place -- assuming all debts are paid in cash. All you need is sufficient liquidity.
I could loan you five quadrillion dollars provided that you also loan me five quadrillion dollars. No currency has changed hands, but we've just increased the world's total outstanding debt by ten quadrillion dollars!