I recently finished Michael Lewis’ most recent book, The Undoing Project: A Friendship that Changed the World and it motivated me to revisit Daniel Kahneman’s Thinking, Fast and Slow. Lewis’ book describes the relationship between Daniel Kahneman and Amos Tversky, two psychologists whose research gave birth to behavioral economics, modern consumer behavior theory and the practical understanding of people’s decision making. He explains the challenges they faced and the breakthroughs that now seem obvious.

As I mentioned, The Undoing Project reminded me how important Kahneman’s book was, probably the most important book I have ever read. It has helped me professionally, both understand consumer behavior and make better business decisions. It has helped me in my personal life, again better decision making in everything from holiday choices to career moves. It helps even to explain the election of Donald Trump or how the situation in North Korea has developed.

In the Undoing Project, two things drove home the importance of Kahneman’s work. First, despite being a psychologist, Kahneman won the Nobel Prize for Economics in 2002. It is difficult enough to win a Nobel Prize (I’m still waiting for the call), but to do it in a field that is not your practice is amazing. The second item that proved the value of Kahneman’s (and his colleague Amos Tversky) work was the Linda Problem. I will discuss this scenario later in this post, but the Linda Problem proved how people do not make rational decisions, myself included. It convinced the mainstream that people, including doctors and intellectuals, consistently made irrational decisions.

Despite the value I derived from Thinking, Fast and Slow, I never felt I learned all I could from it. I found it very difficult to read, the exact opposite of a Michel Lewis book, and did not digest all the information Kahneman provided. Even when I recommended the book to friends, I often caveat the recommendation with a warning it will be hard to get through.

Given the importance of Kahneman’s work and the challenge I (and probably others) have had in fully digesting Thinking, Fast and Slow, I will be writing a series of blog posts, each one summarizing one chapter of Kahneman’s book. I hope you find it as useful as I know I will.

The Linda Problem

As discussed above, the Linda Problem is the research by Kahneman and Tversky that largely proved people thought irrationally, or at least did not understand logic. While I normally like to paraphrase my learnings or put them into examples relevant for my audience, in this case it is best to show the relevant description from The Undoing Project, as the Linda Project was a scientific study that I do not want to misrepresent:

Linda is 31 years old, single, outspoken and very bright. She majored in philosophy. As a student, she was deeply concerned with issues of discrimination and social justice, and also participated in anti-nuclear demonstrations.

Linda was designed to be the stereotype of a feminist. Danny and Amos asked: To what degree does Linda resemble the typical member of each of the following classes?

1. Linda is a teacher in elementary school.
2. Linda works in a bookstore and takes Yoga classes.
3. Linda is active in the feminist movement.
4. Linda is a psychiatric social worker.
5. Linda is a member of the League of Women voters.
6. Linda is a bank teller.
7. Linda is an insurance salesperson.
8. Linda is a bank teller and is active in the feminist movement.

Danny [Kahneman] passed out the Linda vignette to students at the University of British Columbia. In this first experiment, two different groups of students were given four of the eight descriptions and asked to judge the odds that they were true. One of the groups had “Linda is a bank teller” on its list; the other got “Linda is a bank teller and is active in the feminist movement.” Those were the only two descriptions that mattered, though of course the students didn’t know that. The group given “Linda is a bank teller and is active in the feminist movement” judged it more likely than the group assigned “Linda is a bank teller.” That result was all that Danny and Amos [Tversky] needed to make their big point: The rules of thumb people used to evaluate probability led to misjudgments. “Linda is a bank teller and is active in the feminist movement” could never be more probable than “Linda is a bank teller.” “Linda is a bank teller and active in the feminist movement” was just a special case of “Linda is a bank teller.” “Linda is a bank teller” included “Linda is a bank teller and activist in the feminist movement” along with “Linda is a bank teller and likes to walk naked through Serbian forests” and all other bank-telling Lindas.

One description was entirely contained by the other. People were blind to logic. They put the Linda problem in different ways, to make sure that the students who served as their lab rats weren’t misreading its first line as saying “Linda is a bank teller NOT active in the feminist movement.” They put it to graduate students with training in logic and statistics. They put it to doctors, in a complicated medical story, in which lay embedded the opportunity to make a fatal error of logic. In overwhelming numbers doctors made the same mistake as undergraduates.

The fact that almost everyone made the same logic mistakes shows how powerful this understanding is. It proves that our judgment, and thus decision making, is often not logical but does contain flaws. This understanding helps explain many things in life and business that sometimes do not seem to makes sense.

The implications

Once you understand how our judgment is biased, it can help you make better decisions. It can also provide insights into how your customers view different options and why people behave as they do. In future posts, I will explore all of Kahneman and Tversky’s major findings and how they apply.

Key Takeaways

• In the Undoing Project, Michael Lewis writes about the relationship and research of Daniel Kahneman and Amos Tversky, two psychologists who changed the way we understand decision making
• The Linda Problem proved to the non-believers that people made illogical judgments. When given a story about a fictional person and then potential careers for that person, virtually everyone (from students to very successful professionals) chose a persona that was a subset of a broader persona, thus impossible that the former was more likely.
• By understanding how people make judgments and decisions, we can improve our own decision making process and better understand our friends, family and customers.