be cast in stone直接翻译是“刻在石头上”，引申为“无法改变”的意思。

【例句】
The past is cast in stone. Let's move forward together.
过去无法改变，让我们一起继续前进。

Please note that the order of these steps is not cast in stone.
请注意这些步骤的次序不是一成不变的。