That all money is debt, and that the fractional reserve monetary system is a pyramid scheme. Banks lend money they don’t have, money that doesn’t actually exist until they lend it. This is how new money is injected into the system to account for new wealth, i.e., the newly manufactured goods and services presumably created with the loaned capital. But money is loaned with an associated interest rate, so more money must be paid back than was created with the loan. That extra money can only come from additional loans. This is why constant economic growth is vital, since that extra money is the profit without which the lender wouldn’t lend. Finally, since infinite growth cannot be supported indefinitely on a finite planet, the system will inevitably collapse.