It seemed too good to be true – and it was. Worse, banks failed to understand the first principle of risk management: diversification only works when risks are not correlated, and macro-shocks (such as those that affect housing prices or borrowers’ ability to repay) affect the probability of default for all mortgages.
这样的事情看上去太美妙而不可能是真的，但是它确实发生的。更糟糕的是，银行没有理解风险管理的第一原则，也就是分散风险只有在这些风险相互没有关联时才有效，而大规模的冲击（比如影响房价或借贷者还款能力的那些冲击）可能会使所有的抵押贷款都出现不履行债务的情况。