A single greed causes a crash! The 30 billion tragedy of Japan's stock market genius—why do smart people also make mistakes?

Can you imagine? A legendary investor who started with 70 yen and rolled it into a 20 billion yen fortune, only to watch in despair as one extra day of greed turned a 30 billion profit into a bubble. This is not a fabricated story, but a true blood-and-tears account of Japan’s stock market god, Kawagane Zō.

From Rags to Riches: The Seventy-Year Investment Journey of a Poor Boy

The story of Kawagane Zō begins with the most humble start. Before age 30, he wandered through China, London, and other places during the World War I era, working as an accountant and in currency melting businesses, making and losing fortunes. Until he was 31, he decided to change his life—by reading books.

In the Osaka Library, this down-and-out middle-aged man immersed himself daily in economics books, spending three years thoroughly understanding market logic. In 1931, armed with 70 yen borrowed from his wife, he stepped into the stock market, thus beginning his legendary journey.

His success was not luck. Collecting data daily, monitoring economic indicators, and communicating with securities firms—Kawagane Zō honed his skills through the most basic methods. This persistence ultimately led to one investment miracle after another.

Three Classic Battles Capturing the Pulse of the Era

Battle 1: The Iron Sheet Surge

The year World War II ended, Kawagane Zō spotted a detail—people needed temporary shelters. He bought大量 iron sheets, causing their prices to skyrocket dozens of times. While others saw disaster, Japan’s stock market god saw opportunity.

Battle 2: Cement’s Counterattack to 30 Billion

The 1970s oil crisis devastated Japan’s economy, plunging the cement industry into a trough. When Japanese cement stocks fell from over 800 yen to around 100 yen, Kawagane Zō bought in. He predicted the government would boost infrastructure to revive the economy. Three years later, this investment earned him 30 billion yen in profit.

Battle 3: Mine Revaluation Ninefold

In the 1980s, news about the Ryo Kaki mine caught Kawagane Zō’s attention. He personally investigated and studied, reaching a startling conclusion—that this gold mine was severely undervalued. Even Sumitomo Metal Mining, the owner, was unaware. Kawagane Zō quietly positioned himself, and within two months, the stock price soared to nine times his purchase price, earning him another 20 billion yen.

But what happened next is the true legend—and the most important lesson.

The Stock Market God’s Secret Weapon: The “Eight-Tenths Full” Philosophy

The hardest part of investing isn’t buying, but selling. When stock prices soar and the market screams “It will go higher,” Kawagane Zō made a decision most people can’t—selling.

In just three weeks, that stock’s price fell to one-third of his selling point. He perfectly timed the top.

Why could he do it? Kawagane Zō created a famous analogy: selling stocks is like eating—only eating to eight-tenths full is wise.

While everyone else envied the potential for further gains, Japan’s stock market god chose to exit early. It looked like he earned less, but in reality, he avoided a major loss later. This is the core secret behind his repeated success in high-risk industries.

The Tortoise’s Three Principles: Slow is Fast

Besides the “eight-tenths full” rule, Kawagane Zō summarized the “Tortoise’s Three Principles”:

1. Identify potential stocks: Find those with good future prospects that are still unnoticed by the public, and hold them long-term.

2. Independent research: Monitor economic trends daily, gather information personally, and distrust overly optimistic media reports.

3. Avoid excessive optimism: Use only your own funds, and don’t believe the stock market only rises.

He never blindly trusted media news because “by the time the news hits the papers, the stock price is usually near its peak.” His method was simple but the only effective one.

How Greed Devoured 30 Billion? Blood-and-Tears Lessons

However, even Japan’s stock market god couldn’t escape human temptation.

In the late 1970s, international prices of non-ferrous metals surged. Kawagane Zō judged that the Soviet invasion of Afghanistan would intensify the rally and bought heavily. As the market heated up, he surprisingly lost his composure. Driven by greed, he refused to sell, missing the best exit point.

What was the result? Stock prices plummeted repeatedly, and the 30 billion yen profit vanished into thin air. The once-admired “eight-tenths full” stock market god paid a painful price for greed—staying one day too long.

The Final Truth

On the investment path, knowledge can be learned, experience can be accumulated, but the hardest to conquer is always the beast called “greed” inside the human heart. Japan’s stock market god’s lifetime legend and one crushing failure teach us—rationally entering the market and calmly exiting are the measures of risk and reward. Can you hold this ruler steady?