A person's looks are a double-edged sword. Sometimes it works in your favour, sometimes it works against you.

一个人的相貌是一把双刃剑。有时它对你有利，有时又对你不利。

《柯林斯英汉双解大词典》

He has found that humor is a double-edged sword.

他发现幽默是一把双刃剑。

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Let us look at an idiom: kill two birds with double-edged sword.

我们再看一个成语：一举两得/一箭双雕。

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But if that broke, if that wasn't available to him, he could turn to his short sword, which was a thrusting sword, not like the Roman short sword which was double edged and slashing.

但是如果矛断了,他就不能使用矛了,那么他就得使用短剑了,这种短剑也是用来刺的,不像罗马士兵的双刃剑那样用砍的

耶鲁公开课 - 古希腊历史简介课程节选

So control of these international highways brought a great deal of wealth to the area, but the central location was a double-edged sword, because in times of peace it would bring prosperity, but, of course, in times of war the land was perpetually invaded as armies would crisscross the land going off to do battle with the great powers.

对这些国际要道的控制,给这个地区带来了大量的财富，但这处于中心的地理位置也如同一把双刃剑，因为在和平时期它带来繁荣，但，在战乱时期，这块土地常常被侵略,当军队在此刀刃相交,或者经过与强国征战。

耶鲁公开课 - 旧约导论课程节选

Being given three stars could be a double edged sword for hospitals, said Ms Burke.

BBC: Will hospital ratings work?

Frankly, in our opinion the whole matter is a double edged sword.

ENGADGET: E3: RIP? Like, for reals?

The daily deal phenomena is a double edged sword.

FORBES: Do Daily Deals Work For Business? Survey Says Yes