old habits die hard 旧习难改；积习难改；本性难移

【例句】
As the saying goes," old habits die hard", our earnest attempts to break those habits often end in frustration.
正如俗话所说：本性难移，我们认真的努力要改掉它却总以失败告终。

Tom has been a chain smoker for years. You know, old habits die hard.
汤姆是个多年的老烟鬼了。哎，积习难改呀。