a leopard can't change its spots 江山易改，本性难移

“江山易改，本性难移”，汉语成语，意思是人的本性的改变比江山的变迁还要难。形容人的内在秉性难以改变，与英文习语“a leopard can't change its spots或a tiger cannot change its stripes”意思相近，表示“One can't change one's essential nature”。

例句：

我们分手后，他回来找我，试图让我相信他已经变了。但是我知道江山易改本性难移。

After our breakup, he came crawling back, trying to convince me that he'd changed, but I know that a leopard can't change its spots.

他一定还会挂科的，毕竟江山易改本性难移。

He is bound to fail the exam again, a leopard cannot change his spots after all.