Imagine you have a shop. You have this regular customer.
One day he comes to you for an order. He says he's a little short on cash and asks you to finance 10% of the order. You want to keep him as a customer so you say OK. You have a profit margin of 20% so no matter what happens you'll be al right.
After a while he starts to ask for a 50% finance on the order. He promises to pay you back with interest. You concede, but you start to wonder. On paper your balance sheet is looking fine. Your sales are up, the value of your shop increases. Only when you open the cash drawer the amount of IOU's starts to catch the attention.
A while later the customer comes again, and is terribly short on cash. This time he asks you not only finance 100% of the item, but asks you to pay his medical bills as well.
Get the analogy?
The Chinese government is paying for the US imports. America loans the money from the Chinese central bank in order to be able to buy stuff from the Chinese manufacturers.
The real cashflow does not flow from the States to China, it flows from the Chinese Central bank to the Chinese manufacturers via the US. And economy 101 will tell you that a direct insertion of governmental money into the economy equals inflation.
The trade surplus has been very good to China. And security buying by the Chinese central bank acted like a permanent discount on Chinese articles. However now they are finding themselves at the wrong end of the bargain.
In other words, they cannot afford to do nothing.



