In this respect, economists are like doctors, who have to know what a healthy body looks like before they can diagnose disease and prescribe treatment. A good doctor does not intervene arbitrarily in the body’s processes, but only in cases where there is objective proof of a disease and an effective treatment can be prescribed.
从这个角度看，经济学家就好比是医生，在能够诊断病情、开出治疗方案之前，他们必须知道健康的体魄是怎样的。好医生不会肆意干预身体过程，而只有在有客观证据证明存在疾病并且可以开出有效治疗方案的情况下才会干预。