It is easy to change rivers and mountains, but difficult to alter one's ingrained nature or character; old habits die hard.
他虽然嘴上答应改掉懒惰的毛病，但过不了几天又故态复萌，真是江山好改，本性难移啊。
Although he promised to give up his lazy habits, he reverted to his old ways after a few days. Truly, it's easy to change rivers and mountains, but difficult to alter one's fundamental nature.
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