While the central bank can alleviate typical debt crises by lowering real and nominal interest rates, severe debt crises (i.e., depressions) occur when this is no longer possible. Classically, a lot of short-term debt cycles (i.e., business cycles) add up to a long-term debt cycle, because each short-term cyclical high and each short-term cyclical low is higher in its debt-to-income ratio than the one before it, until the interest rate reductions that helped fuel the expansion in debt can no longer continue. In the short-term debt cycle, spending is constrained only by the willingness of lenders and borrowers to provide and receive credit. When credit is easily available, there’s an economic expansion. When credit isn’t easily avail able, there’s a recession. The availability of credit is controlled primarily by the central bank. The central bank is generally able to bring the economy out of a recession by easing rates to stimulate the cycle anew. But over time, each bottom and top of the cycle finishes with more economic activity than the previous cycle, and with more debt. Why? Because people push it—they have an inclination to borrow and spend more instead of paying back debt. It’s human nature. As a result, over long periods of time, debts rise faster than incomes. This creates the long-term debt cycle

短期的债务周期组成了长期债务周期。每一个短期的低点一般都高于上一短期的低点，当利率降到接近0，就无法继续刺激增加信贷。

You will note how the interest payments remain flat or go down even when the debt goes up, so that the rise in debt service costs is not as great as the rise in debt. That is because the central bank (in this case, the Federal Reserve) lowers interest rates to keep the debt-financed expansion going until they can’t do it any more (because the interest rate hits 0 percent). When that happens, deleveraging begins.

借债越来越多，但利率越来越低，所以还款并没有增加多少，但当利率不能再降，也就也就意味着还款压力就上来了，这个时候就要开始去杠杆了。

Remember that money serves two purposes: it is a medium of exchange and a store hold of wealth. And because it has two purposes, it serves two masters: 1) those who want to obtain it for “life’s necessities,” usually by working for it, and 2) those who have stored wealth tied to its value. Throughout history these two groups have been called different things—e.g., the first group has been called workers, the proletariat, and “the have-nots,” and the second group has been called capitalists, investors, and “the haves.” For simplicity, we will call the first group proletari at-workers and the second group capitalists-investors.

钱有交换和存储价值的作用。无产者用时间换钱换生活必需品。资本家用钱生钱来存储财富。