expression, noun
the way of the world; the lay of the land; the inescapable circumstances of life
A set phrase expressing resignation or acceptance of how things inevitably are in life or society. Often used in reflective or philosophical contexts.
世の習いで、金持ちはますます金持ちになる。
It's the way of the world that the rich get richer.
若者が都会へ出ていくのも世の習いだ。
It's just the way of the world that young people move to the city.
世の中 refers to society or the world in a general sense, while 世の習い specifically emphasizes the customary or inevitable patterns of life.
世間 means the world of people or public opinion, whereas 世の習い is more about the natural order or common fate.
Compound of 世 (yo, 'world, society') + の (no, possessive particle) + 習い (narai, 'custom, practice, what is learned'). Literally 'the custom of the world'.