On a scorching September day in 1720, the streets of London were gripped by panic. The wealthy had become beggars, beggars even more destitute. South Sea Company shares, worth 1,050 pounds just six months earlier, had plummeted to 175 pounds. An 80% collapse. History’s first great speculative bubble had burst.

In the midst of this chaos stood a 77-year-old man. He had discovered gravity, laid the foundations of modern mathematics, and translated the workings of the universe into formulas. His name was Isaac Newton, and on that day, he was 20,000 pounds poorer. In today’s value, between 3 and 4 million dollars.

How had one of the world’s brightest minds fallen prey to history’s greatest financial catastrophe?

The answer to this question has been studied in the fields of investor psychology and behavioral finance for over 300 years. Because Newton’s story is not simply one man’s loss, but a crystallized example of the universal weaknesses human nature exhibits when confronting financial markets.

From 1711 to 1720: Anatomy of an Imperial Dream

The South Sea Company’s story began as a plan designed to alleviate the financial burden of England’s war with Spain. Founded by parliamentary decree in 1711, the company agreed to assume 10 million pounds of government debt. In return, it was granted monopoly rights to trade with Spanish colonies.

On paper, it was a clever plan. The government would be relieved of debt interest, the company would profit from South America’s riches. For investors, it seemed an attractive opportunity: both government backing and the tremendous profits colonial trade would bring.

In reality, the company’s commercial operations were never profitable. The Asiento agreement with Spain permitted the company to send only one ship per year. Revenue from the slave trade was insufficient to cover expenses. The company essentially made money by selling stock and managing government bonds. The foundations of a classic Ponzi scheme had been laid, but no one wanted to see it.

A turning point came in 1718: King George I personally assumed chairmanship of the company’s board. The King’s endorsement sent a powerful signal to the market. And this is precisely when Isaac Newton entered the stage.

Newton’s First Move: The Logic of Smart Money

Newton’s relationship with the financial world was not new. As Master of the Royal Mint, he had reformed England’s monetary system. He also invested in government bonds and Bank of England shares. In short, by his era’s standards, he was a sophisticated investor.

When South Sea shares began rising in early 1720, Newton already held some stock in his portfolio. Shares priced at 128 pounds in January climbed to 175 pounds in February, 330 pounds in March, and 550 pounds in April. The mathematical genius’s eye detected an anomaly in these numbers.

In two separate transactions on April 19 and 23, he sold all his South Sea shares. A perfectly timed exit. 100% profit, 7,000 pounds extra in his pocket.

Financial historians view this decision as proof that Newton had recognized the market froth. Smart money had seen the peak and fled. If the story had ended here, Newton would be remembered today not just as a physicist, but also as a masterful investor.

But the story did not end here.

The Return: An Irrational Decision by a Genius

Newton had sold his shares at the end of April. But the market madness did not stop. In May, shares rose to 700 pounds. In June, the 1,000 pound barrier was breached. On June 24, the peak was reached: 1,050 pounds. Nearly twice the price at which Newton had sold.

What was Newton seeing during this period? Every day, his friends, colleagues, and acquaintances spoke of incredible profits. People from every segment of society were buying South Sea stock. London’s coffeehouses talked of nothing else.

One of Newton’s friends, Thomas Guy, sold his shares at exactly the right time, earning 250,000 pounds and using this money to establish Guy’s Hospital. Today it remains one of England’s most prestigious hospitals. Newton, meanwhile, watched the value of the shares he had sold double.

The psychological pressure was immense. Modern behavioral finance literature describes what Newton experienced as: Fear of Missing Out (FOMO), regret aversion, and herding behavior.

Newton, perhaps for the first time in his 77 years of life, made an emotional decision against his own rational judgment. Financial records show that he re-entered positions near the peak, probably at prices around 800–900 pounds.

The Collapse: A Millionaire One Day, Ruined the Next

The first cracks appeared in August. Some major investors started selling. The share price retreated to 800 pounds, then 700, then 600. By September, the collapse had accelerated.

It emerged that the South Sea Company’s commercial operations were unprofitable, that executives had resorted to bribery and manipulation, and that even some members of Parliament were involved.

On September 9, the share price fell to 175 pounds. An 83% drop from the June peak. Newton’s loss was around 20,000 pounds - between $3 and $4 million in today’s value.

The trauma was so deep that Newton banned the words “South Sea” from being spoken in his presence for the rest of his life.

“I Cannot Calculate the Madness of People”

The most famous quote attributed to Newton emerged after this disaster: “I can calculate the motion of heavenly bodies, but not the madness of people.”

This quote summarizes the fundamental principle of behavioral finance: human behavior is not predictable like the laws of physics. Newton could calculate the mathematics of the Solar System flawlessly, but he could not control his own emotions and the psychology of the crowd.

Behavioral Finance: The Psychological Traps Newton Experienced

Modern behavioral finance, built on Daniel Kahneman and Amos Tversky’s Nobel Prize-winning Prospect Theory (1979), provides a solid framework to explain what happened to Newton.

1. FOMO (Fear of Missing Out)

After selling, Newton watched prices double. This was perceived not as “I didn’t gain” but as “I lost potential profit.” Modern research shows FOMO triggers dopamine and cortisol release, suppressing rational thinking and activating emotional decision centers.

2. Herding Behavior

In 1720 London, everyone was buying South Sea stock. Newton likely thought “this many people can’t all be wrong.” Neuroeconomic research shows social conformity activates the brain’s reward centers. Being outside the group is genuinely painful - evolutionarily, it was a survival disadvantage.

3. Overconfidence

Newton had solved difficult problems throughout his life. He may have thought “if I can solve physics, I can solve the market.” Research shows cognitively capable people tend to think they’ll perform equally well outside their areas of competence.

4. Anchoring Bias

Newton bought back shares at 800–900 pounds. Taking the 1,050 peak as reference, 900 may have appeared “discounted.” Yet the real reference should have been the company’s true value.

5. Recency Bias

In May, June, and July, shares rose continuously. Newton may have assumed the trend would continue indefinitely. Yet historical data showed that bubbles always burst.

History Repeating: From South Sea to Modern Bubbles

Human psychology does not change. Similar scenarios have repeated over centuries:

  • Tulip Mania (1634–1637): A rare tulip bulb sold for the price of an Amsterdam house, then collapsed.
  • Dot-com Bubble (1995–2001): Companies with no profits reached trillion-dollar valuations. Nasdaq lost 78%.
  • Housing Bubble (2003–2008): “Prices never fall” belief caused the global financial crisis.
  • Crypto Mania (2017–2021): Bitcoin surged to $69,000, then fell to $15,000. Dogecoin reached $80B market cap as a joke.

All share common denominators: a narrative of new opportunity, “this time is different” rhetoric, quick wealth promises, herd psychology, ignored critics, and sudden collapse.

Neuroeconomics: Brain Chemistry and Investment Decisions

Stanford University research using fMRI brain imaging revealed that the expectation of large gains overactivates reward centers (nucleus accumbens) - resembling cocaine or gambling addiction patterns. Loss threats trigger the amygdala (fear) and insula (pain) regions.

The critical finding: during high-stress moments, the prefrontal cortex (rational thinking) goes offline, and the limbic system (emotional center) takes control. This is exactly what Newton experienced in 1720.

The Importance of Discipline in Investor Psychology

To avoid Newton’s mistakes, behavioral finance suggests clear strategies:

1. Set Rules in Advance

Warren Buffett’s famous rules: “Never lose money.” Pre-established rules reduce emotional impact. If Newton had set a rule like “once sold, never return,” he would not have lost millions.

2. Keep an Investment Journal

Document every decision and your emotional state. Research shows writing itself increases emotional control and helps analyze behavioral patterns.

3. Seek Contrary Views

Combat confirmation bias by actively seeking opposing arguments. Thomas Guy asked “when will this burst?” and sold in time.

4. Think Long-Term

Benjamin Graham: “In the short run the market is a voting machine, but in the long run it is a weighing machine.” Short-term movements trigger emotions; long-term perspective reduces their power.

5. Control Position Size

Never concentrate all assets in a single investment. Newton disrupted his diversified portfolio and bet everything on South Sea.

The Greatest Investment Is Psychological Capital

Isaac Newton discovered the laws of the universe but could not control the laws of his own psychology. Physics is deterministic. Human behavior is chaotic.

The key to success in financial markets is not just analytical intelligence, but emotional discipline. Warren Buffett says, “Be fearful when others are greedy, and greedy when others are fearful.” Easy to say, extraordinarily hard to do.

Newton’s story teaches us this: No matter how high your intelligence, if you lack emotional discipline, you cannot survive in the markets.

Perhaps the best investment is not in your portfolio, but in yourself. Psychological resilience, risk management, discipline, and long-term perspective. These are assets that never lose value in any crash.

The next time you think “everyone’s buying, I should too,” remember Newton. He could calculate the motion of heavenly bodies but could not calculate the madness of people. You, at least, try to calculate your own.