原文（《淮南子•人间训》）
夫禍福之轉而相生，其變難見也。
近塞上之人有善術者，馬無故亡而入胡。人皆吊之。
其父曰：「此何遽不為福乎？」
居數月，其馬將胡駿馬而歸。人皆賀之。
其父曰：「此何遽不能為禍乎？」
家富良馬，其子好騎，墮而折其髀。人皆吊之。
其父曰：「此何遽不為福乎？」
居一年，胡人大入塞，丁壯者引弦而戰，近塞之人，死者十九，此獨以跛之故，父子相保。
故福之為禍，禍之為福，化不可極，深不可測也。
英译 (wiktionaray.com)
It can be difficult to foresee the twists and turns which compel misfortune to beget fortune, and vice versa.
There once was a (father), 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 father 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 fine horse, so everyone congratulated him.
(But) the father said, “Why should I hastily (conclude) that this can not be unfortunate?”
His family had a wealth of fine horses, and his son loved riding them.
One day (the son) fell off the horse, 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)
这是Wiktionary的翻译，我估计是机器翻译，但翻译得不错，比大多数英语专业大学生翻译得好。
另一个版本不是逐字英译，而是用简单的英文讲了一遍那个故事，也供你学习参考：
http://edu.sina.com.cn/en/2009-08-19/162252476.shtml