Meaning: It refers to a loss which may turn out to be advantageous or a gain which ends up being harmful. It suggests that all fortune, good and ill, may be fleeting, and there is no way to know how things will turn out.

Source: "Common Sense Lessons" from Huai Nan Zi: "There was a man who lived by the Great Wall. His horse ran off to the barbarian lands. People all sympathized, but he said, 'Who knows? This may end in good luck.' Months later, his horse returned, accompanied by one from the barbarian lands."

1.Near the Great Wall lived an old man, who had a fine horse. One day the horse ran away to the barbarian territory, and failed to return.

2.When his friends and relatives heard the tale, they all came to comfort the old man.

3.They never expected the old man to say with a lack of concern, "The way I look at it, who knows if having my horse run away might not bring me some advantage!"

4.Several months later, the old man's horse returned, bringing back a horse of the barbarians with it.

5.Again his friends and neighbors all came, this time to congratulate him. But he responded that there was really nothing worth rejoicing over. If something went wrong, he said, the end result could still be disastrous.

6.Regrettably, the old man's words were right on the mark. His son tried to ride the horse from the barbarian lands. Unfortunately, the horse had not been tamed, and it threw the boy to the ground, breaking his leg.

7.Again family and neighbors arrived to express their sympathy. The old man told them, "You needn't worry so much about me. Although it is unfortunate that my son broke his leg, it may turn out to be for the best."

8.A year later, the barbarians attacked and broke through the Great Wall in force. All the healthy young men in the area were called to war, and the vast majority were killed.

9.The old man's son, on the other hand, was spared, because his bad leg kept him out of military service.

10.This story is recorded in Huai Nan Zi. It points out that in all good fortune there may lurk bad, and vice versa, expressing the logic that good and bad fortune are relative, interdependent, and ever-changing.