塞翁失马，安知非福 — “A loss may turn out to be a gain”

In ancient times, an old man living near the frontier lost his horse, which ran away to the land of the Huns beyond the Great Wall. His neighbors came to comfort him, but the old man said, 'How do you know this isn't a good thing?'

A few days later, the lost horse returned, bringing several wild horses with it. The villagers congratulated him, but the old man said, 'How do you know this isn't a bad thing?'

His son, who loved riding, went to ride one of the new wild horses but fell off and broke his leg. Again, the neighbors expressed their sympathy, but the old man said, 'How do you know this isn't a good thing?'

Later, a war broke out, and all able-bodied young men were conscripted into the army. Because the old man's son was lame due to his broken leg, he was spared from joining the war, thus avoiding danger and harm.