The characters combine to create a powerful and self-explanatory image: `[蚍蜉 Ant] [撼 shakes] [树 tree]`. This visual metaphor instantly conveys the meaning of a weak force attempting a foolish and impossible feat against a powerful entity.
The idiom originates from a poem by the famous Tang Dynasty scholar and poet Han Yu (韩愈). In his poem “调张籍” (Teasing Zhang Ji), he wrote the line: “蚍蜉撼大树，可笑不自量” (pífú hàn dà shù, kěxiào bù zì liàng), which means, “For a tiny ant to shake a great tree, is a laughable lack of self-awareness.” This origin firmly roots the idiom in China's rich literary tradition. It's more than just a phrase; it's an allusion that carries the weight of classical literature. It reflects a cultural value of knowing one's place and having a realistic understanding of one's own capabilities (自知之明, zì zhī zhī míng). To be accused of `蚍蜉撼树` is a harsh criticism of one's arrogance and foolishness. A common Western comparison is “tilting at windmills,” from *Don Quixote*. Both describe fighting an unbeatable foe. However, there's a key difference. “Tilting at windmills” can sometimes carry a hint of tragic idealism or romantic folly. 蚍蜉撼树, on the other hand, is almost entirely scornful. It emphasizes the insignificance and absurdity of the challenger, with little room for sympathy. It is the complete opposite of a “David and Goliath” story, as it presupposes absolute and certain failure.
`蚍蜉撼树` is a formal, literary idiom. You won't hear it in casual daily chatter, but it is common in more formal contexts.