你永远不能把过去一笔勾销。

You can never wipe out the past.

《牛津词典》

我必须指出新药的试验很昂贵，而且你永远不能保证成功。

I must point out that trials of new medicine are expensive and you can never guarantee success.

youdao

你永远不能决定给面包的哪面涂黄油。

You can never determine which side of the bread to butter.

youdao

And so the big issue is -- this is what you must never do, but this is what you got to do if your phalanx is broken.

所以现在的大问题是,这也许是你在战场上永远不能做的事,但你在方阵被打散时不得不这么干

耶鲁公开课 - 古希腊历史简介课程节选