Prosody appreciation through a short classical Chinese piece of writing. This is the story behind the idiom, 塞翁失馬, 焉知非（禍）福.
English explanation from Wikitionary
“It can be difficult to foresee the twists and turns which compel misfortune to beget fortune, and vice versa. There once was a old man, skilled in divination, who lived close to the frontier (with his son). One of his horses accidentally strayed into the lands of the Xiongnu, so everyone consoled him. (But) the old man said, “Why should I hastily (conclude) that this is not fortunate?” After several months, the horse came back from the land of the Xiongnu, accompanied by another stallion, so everyone congratulated him. (But) the father said, “Why should I hastily (conclude) that this can not be unfortunate?”. One day (the son) fell off the stallion, and broke his leg, so everyone consoled (the father). (But) the father said, “Why should I hastily (conclude) that this is not fortunate?”
One year later, the Xiongnu invaded the frontier, and all able-bodied men took up arms and went to war. Of the men from the frontier (who volunteered), nine out of ten men perished (from the fighting). It was only because of (the son’s) broken leg, that the father and son were spared (this tragedy). Therefore misfortune begets fortune, and fortune begets misfortune. This goes on without end, and its depths can not be measured. (Wiktionary translation)”