轻车熟路

Origin and story

Han Yu's farewell preface for Master Shi describes a gifted recluse recommended to a military governor. His command of reasoning, historical questions, character judgments, and likely outcomes is compared to four horses drawing a light carriage along a familiar road, with the renowned charioteers Wang Liang and Zaofu attending it. Everything in the comparison makes progress easy: the load, the route, and the skill of those handling it.

The later idiom condenses that image into four characters. Xin Qiji also uses the exact wording in a lyric. Its ease comes from familiarity and practiced ability, not from assuming that an unfamiliar task requires no preparation.