一成不变

yī chéng bù biàn

fixed and unchanging

Character by character

一yī
once

成chéng
formed

不bù
not

变biàn
change

世界上没有一成不变的东西。

Nothing in the world stays the same forever.

Tone: neutral.

From the Book of Rites (王制): a punishment, once carried out, cannot be changed; now 'rigid, fixed'.

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