From
《老子·道德经·第五十八章》:
祸兮福之所倚,
福兮祸之所伏。 (Misfortune - fortune leans upon it; fortune - misfortune hides within it.) One of the most influential passages in Chinese thought, articulating the mutual reversal of opposites (
相反相成). The chengyu
塞翁失马 illustrates the same principle as a story.