江山易改，禀性难移

jiāngshān yì gǎi, bǐngxìng nán yí

[It's easy to change rivers and mountains but hard to change a person's nature; a fox may grow grey, but never good; a sow, when washed, returns to the muck; it is hard to change man's natural disposition than to change rivers and mountains] 政体容易更改, 本性难于变移, 比喻生性风格或既成的事实难以改变