Misfortune and fortune lean on each other.

The text of chapter 58 of the Dao De Jing reads: "禍兮, 福之所倚; 福兮, 禍之所伏. 孰知其極?" — Misfortune, ah, is where fortune leans (倚); fortune, ah, is where misfortune lies hidden (伏). Who knows where it ends? Here the two verbs 倚 (yi, to lean) and 伏 (fu, to lie hidden) are decisive. 倚 is the image of two people leaning back to back, and 伏 is the image of a beast crouching hidden in the grass. Misfortune and fortune do not stand on opposite sides; they sit back to back in the same place, or one crouches inside the other. This idea was later made concrete in the famous fable of "the old man at the frontier and his horse" (塞翁之馬). In that story from the Huainanzi (淮南子), the old man's horse running away seemed a misfortune, but it came back bringing a fine horse; his son breaking his leg riding it seemed a misfortune, but it spared the son from conscription into war. Again and again, misfortune becomes fortune and fortune becomes misfortune.

The English "paradox" entered the language in the 1540s by way of the Latin paradoxum. It comes ultimately from the ancient Greek παράδοξον (paradoxon), a compound of para (beyond, against) + doxa (received opinion, belief). Translated literally, it means "that which runs against common belief, that which defies expectation." Cicero (106–43 BCE), in his Latin work Paradoxa Stoicorum, presented six paradoxes of Stoic philosophy, calling "paradoxa" those propositions that seem contradictory but prove true upon reflection. This tradition was carried into English during the Renaissance. In 16th-century English, paradox was first used to mean "a statement contrary to common sense." Over the 17th and 18th centuries it branched into two senses: the logical paradox (self-referential contradiction) and the rhetorical paradox (a deeper truth within an apparent contradiction). The context in which "paradox" carries the most force today is the latter — "that which seems contradictory yet is true."