double-edged sword

From the notion that if two sides of the same blade are sharp, it cuts both ways. The metaphor may have originated from the Arabic expression سَيْفٌ ذُو حَدَّيْنِ‎ (sayfun ḏū ḥaddayni, “double-edged sword”).

The metaphor is first attested to in English in the 15th century.

It is not to be confused with a double-ended sword.

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double-edged sword (plural double-edged swords)

1. Used other than figuratively or idiomatically: see double-edged,‎ sword.
2. (figurative) A benefit that is also a liability, or (a benefit) that carries some significant but not-so-obvious cost or risk.
   • 2020 June 23, Tiffany Hsu, “Ad Boycott of Facebook Keeps Growing”, in New York Times‎:

     He added: “Facebook is a double-edged sword. You don’t want to support it, but you have to use it in order to reach a large audience.”

   • 2021 February 9, “The double-edged sword of movie stardom remains the same as it ever was: when a persona is so fixed in the public mind, it's what people love you for, and it becomes difficult to deviate from.”, in BBC‎:

   • 2021 July 28, Ben Jones, “When BR got cracking after withdrawal of 'Blue Trains'”, in RAIL, number 936, page 32:

     Of course, social media is a double-edged sword, and the opportunity for passengers to communicate their feelings to media teams is not always a happy one.

3. (figurative) A neutral principle that has applications that may be either positive (beneficial) or negative (adverse) to one's own interests.

   The unintended ambiguity of the phrase was a double-edged sword: it spurred litigation but it also ended up shielding good-faith actors.

• dual-edged sword
• two-edged sword

• dual-use technology

• Midas
• Trojan horse
• a blessing and a curse
• blurse
• be careful what you wish for