The Elliott Wave Theory, the subject of this book, is a law of stock market movements discovered by a man named Elliott in the late 19th century.
This theory was on the verge of being abandoned after Elliott's death, but it began to gain traction as an effective technique for predicting stock price movements after it accurately predicted the Black Monday stock market crash on Wall Street in 1987.

Eliot said that although we cannot know exactly why, we can know from experience that there is some law that moves the universe or all things around us.
The sun sets and rises, spring comes and summer comes, fall and winter appear in succession, the orderly change of night and day, and the change of cold and hot seasons would be impossible without these laws that govern all things.

And since stock prices in the stock market, which is our main concern, are also moved by humans and are also a part of the universe, it is certain that the laws that govern the universe and all things will also apply to the stock market.

Elliott did not simply discover the laws governing the movements of the stock market through empirical and intuitive methods. Rather, he discovered the laws governing the movements of stock prices in the stock market after a long period of research and examination, collecting detailed data on the stock price movements of the past 75 years in monthly, weekly, daily, hourly, and even 30-minute units.
--- From the preface

However, the decisive factor that led to Elliott's theory taking the top spot among various stock market prediction techniques as it is today was the great crash of the U.S. stock market, known as 'Black Monday'.

In October 1987, the U.S. stock market experienced its worst crash ever.
The prices of all stocks that had previously been showing a gentle upward trend collapsed and continued to fall endlessly.
Unlike our country, where daily stock price movements are not limited to the upper and lower limits, the decline in that single day was almost equal to the increase in the previous six months.
There was even an incident where an investor who suffered huge losses shot and killed a securities firm employee who had recommended that he buy stocks.

--- p.24