In this book, I will argue the following facts:
First, rational behavior is much more widespread than we realize, and can appear in unexpected places, like the mind of a sexually curious teenager.
Second, economists' belief in rationality (the word "belief" seems appropriate) provides practical insights.
In fact, we cannot understand the world if we do not understand the rational choices that underlie our actions.
Drug addicts and teenage murderers can be rational too.
The phenomenon of urban sprawl and urban hollowing out, in which cities spread out in an uncontrolled manner, is also clearly rational.
So, are the endless meetings in the office and the bizarre injustices we experience during corporate life justifiable? Of course.
'Rational choice theory' is like an X-ray photograph that clearly reveals human life.

--- p.15~16, from “Prologue_Every choice has a good reason”

A recent study by researchers at Johns Hopkins Medical Center found that the number of young people between the ages of 12 and 24 who had engaged in oral sex more than doubled between 1994 and 2004.
…omitted… “What are the costs, benefits, and consequences of oral sex?” Perhaps the benefits are so obvious that it’s almost embarrassing to even explain them.
Especially for people who engage in oral sex.
On the other hand, the alternative to oral sex, regular intercourse, has become more expensive than in the past.
Because of the spread of AIDS.
HIV, the virus that causes AIDS, is much more likely to spread through regular sex than oral sex.
Many teenagers know that.
A recent study on sex education found that American children learn more about AIDS than about contraception.
--- p.22~23, from 「CHAPTER 1 Smart Sex Chosen by Wise People _ Rational Choice Theory」

Poker seems to be about psychology, not math.
Could there really be a rational strategy behind such tricks and counter-tricks—one that involves no attempt to read the opponent's mind or penetrate their psychology? Could pure mathematics explain such tricks? Von Neumann thought so.
Von Neumann's research in game theory reached its peak in 1944 with the publication of his book, "Game Theory and Economic Behavior," with Oskar Morgenstern.

--- p.78~79, from 「CHAPTER 2 Can life be predicted like a game_Game theory」

If women prefer wealthy men, as George Gershwin, evolutionary biologists, and Internet daters suggest, they should flock to places with a large number of wealthy men.
The city is a place that fits those conditions.
Men are not as interested in marrying wealthy women, so they are not as interested in cities as women.
When rents rise, men who are not good at earning money return to the countryside before women who are not good at earning money.
Or maybe you don't even think about entering the city in the first place.
This is what Lena Edlund of Columbia University argues.
Her argument is summarized as follows:
First, when looking at the male-to-female ratio, there are always fewer men in cities than in rural areas.
This phenomenon was observed in 44 of the 47 countries she surveyed (the remaining three countries had similar gender ratios in both urban and rural areas).

148~149, from “CHAPTER 3 Why do great women marry ordinary men? _The Law of One Thing and One Family”

But according to tournament theory, an $800 million salary doesn't necessarily motivate Eisner—to make that much extra money for Disney shareholders.
If this money actually motivated his subordinates to work hard and become the next Eisner, then it was worth it.
If Eisner's salary motivated Disney employees to make more than $800 million, then paying him $800 million might have been a reasonable decision for Disney shareholders, even if he spent all day with his feet up on the desk watching Tom and Jerry.
This illustrates an interesting aspect of tournament theory.
In other words, a CEO's salary may be unrelated to his performance.
From this perspective, the CEO is excluded from the productive flow.
Although they are merely 'symbolic figures' like queens, they are compensated more than those who do important work.

--- p.199~200, from 「CHAPTER 4 Why Idle Bosses Get Paid More_Tournament Theory」

Margaret and Sarah were attacked by a stranger in a crowded downtown area during rush hour.
But the two could not meet.
Fortunately, Sarah survived, but Margaret did not.
… Omitted… Sarah almost suffered the same fate as Margaret.
She, like Margaret, was attacked by a stranger.
But the place where she was attacked was not a secluded park.
Reginald Jones, who attacked her, used 15th Street in Washington, D.C. as the point of attack.
On a muggy July evening, people were outside, unable to bear the heat.
Some people wandered around the bars, restaurants and ice cream shops on 17th Street, while others headed to the Whole Foods supermarket.
…omitted… Jane Jacobs, who studied urban economics, argued that neighbors act as “eyes on the street” to protect us from crime, as evidenced by the cases of Sarah and Margaret.

--- p.233~236, from 「CHAPTER 5: Determining Where Prejudice Lives_Chessboard Model」

Their research team created 5,000 fake resumes by modifying contact information, addresses, and other information from resumes posted on job sites.
Some resumes have been made more attractive by adding things like part-time work experience, computer certifications, and military service records to create a more attractive 'quality resume'.
On the other hand, other resumes were ordinary and had no special touches.
The research team then randomly assigned names to the resumes.
Some resumes included Black names like Tyrone Jones and LaToya Washington.
Other resumes featured white names like Allison Walsh and Brendan Baker.
…omitted… The results were dismal.
People with white names were called for interviews 50 percent more often than people with black names.
In an experiment with such a large sample size (in a world without bias), the odds of this happening by chance are less than one in ten thousand.
Just as the fake employers in Pryor's experiment rejected applicants as soon as they saw the word "purple," the real employers also rejected applicants as soon as they saw a black name.

--- p.262~263, from 「CHAPTER 6: The Tragic Reality Brought About by Rational Choices_Rational Discrimination」

The more knowledge-intensive an industry is, the more it is concentrated in smaller areas.
Occupations that hire workers with specific skills also tend to be concentrated in the same area.
Economists examined more than 4,000 industrial innovations developed across the United States.
As a result, more than half of the cases occurred in three regions.
California, New York, New Jersey, and Massachusetts are hotbeds of innovation.
Most industries were concentrated there.
This concentration is even more pronounced in high-tech industries.
In the computer field, about half of the innovations took place in California.
In the pharmaceutical field, about half of all innovations occurred in New Jersey, a state with less than 3 percent of the U.S. population.
It's a really sharp world.
And the world will become more pointed.
--- p.309~310, from 「CHAPTER 7 Why are city houses expensive_Spillover」

One surprising fact: Since the likelihood of any vote affecting the outcome of an election is extremely low, there's little benefit to voting with sufficient information.
So why would anyone bother to get information about the candidates? Let's compare voting to buying a car.
If you bought a car because you thought it was safe and fuel-efficient, you could pay a dear price for that mistake.
On the other hand, if you elected George W. Bush because you mistakenly believed he would support same-sex marriage, you suffered no harm, despite that mistake, because your vote did not determine the outcome of the election.
…omitted… From a rational choice perspective, the typical voter is ignorant, that is, ‘rationally ignorant.’
--- p.340~341, from 「CHAPTER 8 Why Strange Candidates Get Elected_Politics and Choice」

“How did our ancestors wipe out the Neanderthals?” Neanderthals survived for over 200,000 years, even enduring the brutal cold of the last Ice Age.
They were large and strong, with large brains, but for some reason, they disappeared only a few thousand years after modern humans appeared in Europe about 40,000 years ago.
…omitted… Some paleontologists claim that Neanderthals used language and had the same intelligence as their rivals, Homo sapiens.
From a 'rational' view of history, it seems that Neanderthals did not practice 'division of labor'.
The value of division of labor has been explained previously.
Division of labor is widespread in modern society.
As I explained before, the cappuccino I always drink is made with many hands.
Without the people who developed electricity, steel casting, and the paper cup, as well as the miners who extracted the coal needed to produce electricity, the farmers who grew the coffee beans, and the dairy farmers who raised the milk cows, we wouldn't even be able to dream of a cappuccino.

--- p.396~397, from 「CHAPTER 9 How are wealthy countries created? --- p. Economic growth」