How to Read “Use a thief to guard against thieves”
Nusubito no ban ni wa nusubito wo tsukae
Meaning of “Use a thief to guard against thieves”
This proverb means that using someone who knows the same tricks is the most effective way to prevent wrongdoing.
Just as catching a thief requires someone who fully understands a thief’s psychology and methods, preventing fraud or problems in any field works best when you place someone familiar with that world as a supervisor or manager.
People use this expression because of a simple reality. No matter how honest or serious an outsider is, they cannot detect clever wrongdoing if they don’t know the actual tricks and loopholes.
Someone from the same world knows exactly where the gaps are, what excuses get used, and which moments are dangerous.
Today, this wisdom appears in the security industry when former hackers help develop defense systems. Financial institutions also place industry veterans to monitor fraudulent transactions.
This proverb teaches the importance of practical experience, not just moral purity.
Origin and Etymology
The exact first written appearance of this proverb is unclear. However, people likely used it already during the Edo period.
Looking at the phrase structure, the core idea seems contradictory. It suggests using a criminal, a “thief,” as a “guard” or watchman.
This expression probably emerged from actual crime prevention wisdom. In Edo period towns, systems developed to protect community safety, including fire watches and night patrols.
Within these systems, practical experience showed that someone who knew theft methods inside and out could spot a thief’s entry routes and targets.
This thinking also connects to the Eastern philosophy of “fighting poison with poison.” Strategic thinking that understands the enemy’s nature and turns it against them appears in military texts too.
Someone who knows the same world can exploit its weaknesses and blind spots. This wisdom based on human observation crystallized into a proverb.
Practical wisdom cultivated in common people’s lives became established as concise, memorable words. It has been passed down not just for crime prevention, but broadly as a lesson about using human resources.
Usage Examples
- We should place someone with long sales experience to check for internal fraud. As they say, use a thief to guard against thieves
- Many cybersecurity experts being former hackers is a typical example of use a thief to guard against thieves
Universal Wisdom
This proverb has been passed down because it touches on an essential human truth. Knowledge and experience have both “light sides” and “shadow sides.”
Those who know both become the deepest understanders.
Completely honest people struggle even to imagine malicious intent. They assume others won’t do what they themselves can’t think of.
But someone who has actually faced temptation and knows that world’s logic understands human weakness and cunning from experience. They can detect real danger without being fooled by surface excuses.
This wisdom shows depth of human understanding. People are neither completely good nor evil. They change depending on circumstances and position.
Rather than excluding those who made past mistakes, their experience gets used for society’s defense. This thinking contains deep insight into humanity and a culture that values practical wisdom.
The proverb also teaches the importance of “knowing your enemy.” Without standing from the same viewpoint, you cannot create true countermeasures.
Good intentions alone cannot protect the world. Sometimes you need the courage to borrow power from those who know the shadow world. This realistic view of human nature lives here.
When AI Hears This
Making a thief the guard seems contradictory at first. But considering game theory, it becomes surprisingly rational strategy.
The key is “information asymmetry.” Regular people who don’t know theft methods cannot spot which places get targeted or what gaps exist.
Meanwhile, thieves can instantly judge entry routes and defense weaknesses. This isn’t just experience difference. They possess the attacker’s thought process itself.
More interesting is how it solves the “commitment problem.” Normally you’d worry “won’t the former thief betray us?” But here’s the paradox.
By making a thief the guard, he changes his position to “the defending side.” If he betrays, the employer knows all his methods, so he gets suspected first.
Betrayal costs become overwhelmingly higher than for regular guards. This is a “self-binding mechanism” where your own expertise constrains you.
Modern cybersecurity uses the same principle. Security companies hire former hackers because they understand attacker thought patterns.
They find vulnerabilities through penetration testing. But simultaneously, their reputation and position function as monitoring devices.
Defense works best with someone who knows attack logic from the inside. This paradoxical equilibrium is security’s essence.
Lessons for Today
This proverb teaches modern people to see the value of people and experiences from multiple angles.
Don’t simply exclude those who failed in the past or took detours. Recognize that their experience can become a valuable asset in certain situations.
If you want to prevent problems in your organization, listen to voices of people who know that field’s inside story.
Surface rules and idealistic theories alone won’t reveal real loopholes. Wisdom from people who know the field and experienced both sides of the industry creates effective countermeasures.
This proverb also teaches how to use your own experiences. If you faced difficulties or temptations in the past, that experience is never wasted.
It becomes power not just to avoid repeating mistakes, but also to guide others away from the same traps.
What matters is acknowledging human complexity. No perfect good people exist. Experience contains both light and shadow.
Understanding both and using them as practical wisdom requires flexibility. That flexibility becomes the power to survive in modern society.
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