That means interest rates have got to be high enough that they’re a good return for the creditor, without being so high that they’re bad for the debtor. In the US, we recently came out of a long free money environment in which interest rates were nil and real interest rates went to -1.7%. And through this, we increased our debt to GDP ratio — the government went into a lot of debt so they could write checks for a lot of things. As debts rise relative to incomes that are supposed to support the debt, this becomes a difficult balance. And in a classical debt cycle, you inevitably reach a point where you have to borrow to service your debt. That can lead to a debt spiral and an economic heart attack.