双刃剑 Double-edged sword。

Its a double-edged sword.它(这种技术)实际上是一把双刃剑。

At the very start, athletic sport is a double blade sword.竞技体育从一开始，就是一把双刃剑

A metaphor used to refer to something that has both advantages and disadvantages, and positive and negative effects.报复本身就是一把双刃剑, 你放过他吧。