(Extracted from ThoughtCo.)
Sāi Wēng lived on the border and he raised horses for a living. One day, he lost one of his prized horses. After hearing of the misfortune, his neighbor felt sorry for him and came to comfort him. But Sāi Wēng simply asked, “How could we know it is not a good thing for me?”
After a while, the lost horse returned and with another beautiful horse. The neighbor came over again and congratulated Sāi Wēng on his good fortune. But Sāi Wēng simply asked, “How could we know it is not a bad thing for me?”
One day, his son went out for a ride with the new horse. He was violently thrown from the horse and broke his leg. The neighbors once again expressed their condolences to Sāi Wēng, but Sāi Wēng simply said, “How could we know it is not a good thing for me?” One year later, the Emperor’s army arrived at the village to recruit all able-bodied men to fight in the war. Because of his injury, Sāi Wēng’s son could not go off to war, and was spared from certain death.
(Extracted from Baidu baike)
在靠近边塞的人中，有一位精通术数的人。他家的马自己跑到胡人那里去了，大家都来慰问他。这位父亲说：“为什么就知道不是福运呢？”过了几个月，他家的马带领着胡人的骏马回来了，大家都祝贺他。这位父亲说：“为什么就知道不是祸端呢？”家里有钱又有骏马，他的儿子喜欢骑马，有一次从马上摔下来折断了大腿骨。大家都慰问他，这位父亲说：“为什么就知道不是福运呢？”过了一年，胡人大举侵入边塞，男子健壮的都拿起弓箭参战，塞上参战的人，十个死九个，不死的都是重伤。唯独他的儿子因为腿摔断了的缘故，父子得以保全性命。所以福可变为祸，祸可变为福，这其中的变化难以捉摸，深不可测。