How to Read “Yesterday’s enemy is today’s friend”
きのうのてきはきょうのとも
Meaning of “Yesterday’s enemy is today’s friend”
This proverb means that even someone you opposed can become your ally when circumstances change.
In human relationships, the distinction between enemy and ally is not fixed. It changes flexibly based on position, situation, and shifting interests.
This saying is used when rival businesses form partnerships. It applies when opposing organizations unite for a common goal.
It also fits when personal conflicts resolve and relationships become friendly.
The reason people use this expression is to view relationship changes positively. It emphasizes the importance of building new connections without clinging to past conflicts.
In today’s globalized world, this proverb feels more relevant than ever. We see it in international relations and corporate alliances on a larger scale.
This saying teaches us the importance of rethinking human relationships with flexible thinking.
Origin and Etymology
The exact origin of this proverb has several theories, with no definitive source identified.
However, the most credible explanation traces it to relationships among warlords during Japan’s Warring States period.
During that era, it was common to fight someone to the death one day and form an alliance with them the next.
Situations involving territory and power changed constantly. Yesterday’s enemy becoming today’s ally was a realistic choice for survival.
The relationship between Takeda Shingen and Uesugi Kenshin is particularly striking. They fought fiercely at Kawanakajima.
Yet when the Takeda clan suffered a salt shortage, Uesugi Kenshin sent them salt. This story gave birth to another saying, “sending salt to the enemy.”
Such relationships among warlords created the recognition that the line between enemy and ally is not absolute. This background likely shaped this proverb.
During the Edo period, the merchant world also saw competitive relationships change with circumstances.
The proverb spread beyond samurai society and became widely used among common people.
This expression succinctly captures the fluidity of human relationships. It reflects the realistic Japanese view of human nature across generations.
Usage Examples
- Two rival companies announced a partnership facing an industry crisis. It’s truly “Yesterday’s enemy is today’s friend.”
- I often clashed with him in school, but now we’re cooperating on the same work project. “Yesterday’s enemy is today’s friend” is well said.
Universal Wisdom
This proverb has been passed down for generations because it brilliantly captures the essential fluidity of human relationships.
We use the words “enemy” and “ally,” but this distinction is merely a temporary framework we create.
Human nature constantly changes. The other person, yourself, and your circumstances are always moving.
What’s interesting is that this proverb doesn’t deny conflict. Rather, it assumes conflict exists while teaching that it won’t last forever.
When people become emotional, they feel current hostilities will continue forever.
But looking back at history, countless nations that once fought fiercely became strong allies. On a personal level, school rivals often become lifelong friends.
This proverb contains deep trust in human adaptability and flexibility.
People can reorganize relationships according to circumstances and build new bonds. That ability is the driving force that has helped humanity overcome various difficulties.
Having the courage to accept change without being bound by fixed ideas of enemy and ally—perhaps that’s what it means to live humanly.
When AI Hears This
In the 1980s, political scientist Robert Axelrod conducted an experiment with surprising results.
He had computer programs compete against each other, repeating cooperation and betrayal. The goal was to find which strategy gained the most benefit.
The winner was the simplest strategy: “tit for tat.” Its rules were straightforward.
Always cooperate on the first move. From the second move onward, simply copy what the opponent did last time.
If they cooperate, you cooperate. If they betray, you betray back. Crucially, if a betrayer returns to cooperation, you immediately forgive and cooperate again.
This strategy is mathematically optimal because it balances retaliation and forgiveness.
A constant cooperator gets exploited by betrayers. A constant betrayer becomes isolated with no cooperation from anyone.
But tit for tat retaliates against betrayal, so it’s not taken advantage of. Simultaneously, when opponents reform, it immediately rebuilds cooperation, maximizing long-term total benefits.
For example, with 100 trading opportunities, eternal hostility after one betrayal loses 99 chances for cooperative profit.
But immediate forgiveness allows both parties to gain benefits for the remaining 98 rounds.
In other words, the attitude of “Yesterday’s enemy is today’s friend” is not emotional generosity. It’s the most rational result of cold cost-benefit calculation.
The flexibility to turn enemies into friends is the strongest survival strategy in evolution.
Lessons for Today
This proverb teaches modern people the importance of “tolerance” and “flexibility” in human relationships.
In today’s society with developed social media, it’s easy to view someone you once opposed as an eternal enemy. However, that also narrows your own possibilities.
If you’re currently in conflict with someone, will that relationship truly never change?
When circumstances shift, the day may come when you cooperate with that person. Don’t cling too much to past conflicts.
Leave room in your heart to build new relationships. That’s not weakness—it’s the wisdom of a mature adult.
In the business world, relationships with competitors constantly change. Today’s rival becoming tomorrow’s partner is not unusual.
Don’t fall into rigid thinking. Maintain an attitude that positively accepts change.
That becomes the strength to survive in our increasingly complex modern society. Human relationships are like a flowing river.
The same water never flows twice.
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