Alea iacta est (Latin: "The die has been cast") is a Latin phrase attributed by Suetonius (as iacta alea est [ˈjakta ˈaːlea est]) to Julius Caesar on January 10, 49 BC as he led his army across the River Rubicon in Northern Italy. With this step, he entered Italy at the head of his army in defiance and began his long civil war against Pompey and the Optimates. The phrase is still used today to mean that events have passed a point of no return, that something inevitably will happen.

可能是当时的一句俗谚，翻译成“箭在弦上，不得不发”也可以

没看懂啊