"A double-edged sword" is a common idiom used to describe a situation, action, or decision that has both significant advantages and disadvantages, or positive and negative consequences. It implies that the same thing can be beneficial and harmful at the same time.
It seems simply to be a figure of speech. A double-edged sword literally cuts both ways. One of the earliest attestations in the OED (Oxford English Dictionary) for "double-edged" comes from a 1687 poem by John Dryden, The Hind and the Panther:
Your Delphic sword, the Panther then replied,
Is double-edged, and cuts on either side.
That brought out another idiom: The Golden Mean (中庸之道, which we all know well)
Everything has a limit, Excessive indulgence in, or pursuit of, any 'good' thing—such as food, work, or even kindness often leads to negative outcomes, demonstrating that moderation is crucial for sustainability. When pleasurable or beneficial activities go beyond a certain point, they can cause harm, exhaustion, or diminishing returns.
- From online with editing
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What triggered me to think about "a double edged sword" was a WXC post (click here to see: 現實很殘酷：地位是由錢決定的) two days ago. I felt uncomfortable enough to voice my concerns under it, even knowing that I'm the "black sheep" there. 
Yes, we all need money to live and enjoy our lives, and some people also enjoy power over others, be it political or personal.
But look at what excessive money and power brought to some people in reality, especially in corrupted societies, don't you see and agree both are double edged swords?
I'd rather follow "the Golden Mean" and be modest in life for myself.
Wish you and your families all a happy fire horse year, with good food and laughter on this Chinese new year eve.
But, please remember, even healthy food can be a double edged sword if consumed too much. 
