Central banks can't save the markets from a crash. They shouldn't even try

``A signal that borrowing costs would remain at rock bottom was all it took. After Black Monday and Wobbly Tuesday, the markets recovered to regain almost all their recent losses. It was just as if they had said to themselves: who cares if China's economy is slowing; the "Greenspan put", which so famously propped up US stock markets during the 1990s and early 2000s with one interest rate cut after another, is still in operation.''