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Thinking, Fast and Slow - Book Review

1 September 2012

Dr. Moria Levy

The book "Thinking, Fast and Slow," authored by Daniel Kahneman in 2011, offers a comprehensive exploration of his doctrine, with significant reference to Prospect Theory, the Nobel Prize-winning concept. Kahneman, a cognitive psychologist, delves into his own experiences, particularly his reserve service in the IDF, infusing the book with examples from Israel. Dedicated to his late collaborator Amos Tversky, the book introduces the two systems in our brains, System 1 and System 2, unveiling the reasons behind seemingly irrational human behavior. Unlike populist works, this profound and instructive book clarifies human behavior, covering topics such as thinking systems, biases in decision-making, and value theory.

The book encompasses the following topics:

  1. Thinking Systems

    a) System 1: The Fastest

    b) System 2: The Slow

  2. Biases in Decision Making

  3. Value Theory

  4. Summary

This summary captures the core of the main idea, emphasizing critical points while acknowledging the richness of examples in the book. Written in an engaging and personal style, the summary is an introduction, encouraging readers to explore the complete work for a more in-depth understanding. Happy reading!

Thinking Systems

As individuals, we often make decisions that may seem irrational from a rational standpoint. What adds intrigue is the realm of systematic errors, commonly known as biases, occurring under specific circumstances rather than mere mistakes.

The exploration of thinking systems—System 1 and System 2—is rooted in this premise. Although initially introduced by psychologists Stanovich and West, the terminology developed considerably from Kahneman. The analysis of thinking systems revolves around examining biases linked to our intuition. The delineation of two systems operating differently and at distinct times not only elucidates these biases but also sheds light on numerous cognitive behavioral theories propounded by various scientists throughout the past century.

System 1: The Fastest

System 1, as termed by Kahneman, operates automatically, swiftly, almost effortlessly, and without a sense of control. For instance, when asked about 2x3, the immediate answer of 6 is "pulled out" without recalculating, showcasing the efficiency of System 1. In contrast, when faced with a question like 17 x 324, beyond its capacity, System 1 defers to System 2 for processing.

This system governs our skills, including what we identify as "gut feelings" and intuition. However, it is also responsible for biases in decision-making, detailed below.

Key features of System 1 (percentages indicate significant weaknesses that warrant recognition):

  • Generates impressions, feelings, and tendencies, which transform into beliefs, references, and intentions when integrated by System 2.

  • Operates automatically and swiftly, requiring little or no effort.

  • It can be "programmed" by System 2 to draw attention to specific behavioral patterns.

  • Executes skillful responses; develops intuition through training.

  • Constructs a coherent pattern of ideas and associations in our minds.

  • % Associates a sense of cognitive ease with illusions of truth, positive feelings, and reduced vigilance.

  • Distinguish the ordinary from the surprising.

  • Infers causes of events and attributes intentions.

  • % Neglects ambiguity and diminishes doubts.

  • Biased toward belief and agreement.

  • % Causes exaggerations, such as evaluating people based on existing information, known as emotional consistency (halo effect).

  • % Focuses on existing evidence and disregards missing evidence (WYSIATI).

  • Establishes a basis for evaluations.

  • Represents sets of norms and prototypes (groupings) without integrating.

  • Coordinates and links different intensities (e.g., connecting a loud voice with something significant).

  • % Sometimes substitutes a posed question with an easier one to facilitate an answer (mental shotgun).

  • More responsive to changes than the situations themselves (value theory below).

  • % Attributes excessive weight to things with low probability.

  • Demonstrates reduced sensitivity to quantity (psychophysics).

  • % Is more responsive to losses than gains (loss aversion).

  • % Heavily relies on the past to make decisions about the future.

  • % Is influenced by associations (priming effect).

(From the book - page 105)

System 2: The Slow

System 2 is responsible for the mental actions required for decision-making, involving concentration, calculations, and more. When contemplating decisions about ourselves, we tend to believe we engage in sound decision-making through systematic thinking and carefully considering various options. We want to think that our brains operate according to System 2.

However, it turns out that this is only sometimes the case. System 1, the front-end system, responds first, while System 2, also known as lazy (since it prefers action only when necessary), oversees the activity of System 1. System 2 comes into play only when it determines that no other choice is viable. Hence, System 2 is also called the "voluntary system" and operates selectively.

Key features of System 2 (percentages indicate significant weaknesses that merit recognition):

  • Controls System 1 activity.

  • Considers alternatives.

  • Helps locate relevant knowledge within our memory base.

  • Possesses analytical capabilities.

  • Makes decisions based on a broad foundation.

  • % Operates slowly, to the extent that relying on it alone is impractical.

  • Even when deciding to engage System 2 and succeed, System 1 can still influence us and impact our emotional state during decision-making. A notable example is comparing the lengths of the following lines:

The feeling induced by System 1 is that the line with the arrows pointing outwards is longer, even if System 2 has trained us to think otherwise. We may provide the correct answer but still need help to believe in it.

  • % Focuses on one (almost) simultaneous activity, disregarding other occurrences during focused tasks (illustrated by the famous example of the unnoticed gorilla in the attention game).

  • % Because it demands concentration, it hinders simultaneous functioning in other dimensions. For instance, engaging in System 2 operations makes us less inclined to be sociable and make a positive impression on those around us.

  • Knows how to follow rules and accurately compare objects in multiple dimensions simultaneously.

  • % Abundant from a good mood that induces complacency and reduces System 2 activation.

Biases in Decision Making

Most biases in decision-making arise from the behavior of System 1. Here are some representative examples:

  • Law of small numbers: Decisions often rely on small, non-representative samples, even by researchers who should know better. [These biases originate from the nature of System 1's activity.]

  • Anchoring effect (1): Decision-makers anchor their decisions to nearby provided information. For instance, answers to unrelated questions can be influenced by each other, serving as anchor points.

  • Anchoring effect (2): Similar effect with a connection between questions, influencing responses based on prior knowledge. [These biases result from the nature of System 2's activity.]

  • Stereotypes: Decisions are often made based on assumptions and stereotypes that don't necessarily reflect reality. [These biases stem from the nature of System 1's activity.]

  • Preferring the least over the most: Decision-makers sometimes make suboptimal choices due to additional information that should seemingly have no effect. [These biases are rooted in System 2's activity.]

  • Mean tune: The tendency to overlook the influence of both talent and luck in extreme success or failure. [These biases arise from the integration of the nature of systems activity 1 and 2.]

  • Excess self-confidence and the illusion of knowledge: Familiarity with a topic can lead to overconfidence and biased decision-making, particularly in forecasting. [These biases originate from the nature of System 1's activity.]

  • Introspection / Excess Optimism: Personal involvement can lead to biased decision-making, and external perspectives can help overcome this bias. [These biases result from the nature of System 1's activity.]

These examples are just a glimpse; many more are discussed in the book. The systematic explanation of these phenomena based on the activity of Systems 1 and 2 is a highlight of the book.

To mitigate biases, it is recommended to follow these four steps when dealing with intuitive errors:

  1. Decide in principle, irrespective of specific conditions.

  2. Assess the degree of correlation (influence) of particular conditions on the decision.

  3. Consider a decision appropriate to the case and conditions.

  4. Adjust the answer based on the correlation level.

Value Theory

Understanding value theory forms the foundation for comprehending the decision-making process delineated through System 1 and System 2. While not an exhaustive exploration of prospect theory, this summary aims to outline its essential aspects. Published in 1979 by Kahneman and Tversky, both psychologists, value theory marked a departure from utility theory, the predominant framework for decision-making until then, as it shifted the focus from how decisions should be made (utility theory) to how decisions are made in practice, aligning with the insights from Systems 1 and 2.

To illustrate the disparity between utility theory and value theory, consider the following examples:

  1. Positive Scenario:

    a) Choose between a guaranteed 50 USD or a 50% chance to win 100 USD in a coin flip (with no loss in the "tails" scenario).

    b) Despite economic equivalence according to utility theory, most people exhibit risk aversion and prefer the assured win.

  2. Negative Scenario:

    a) Choose between paying 50 NIS outright or taking a 50% chance to avoid paying anything but facing a 50% chance of paying 100 NIS.

    b) Contrary to utility theory, individuals tend to favor taking a risk over a certain loss, even if the amount is lower.

Prospect theory delves into both positive and negative decision-making scenarios, offering a nuanced understanding. Critical aspects of the theory include:

  • Prospect Significance: The term "Prospect" refers to chance, indicating that changes in probabilities (favorable or unfavorable) significantly impact decision-making.

  • Factors Influencing Decisions: Three main factors shape decision-making outcomes—certainty, the nature of the decision (loss or gain), and the magnitude of the amount.

While the theory is intricate, this overview focuses on the core elements of explaining decision-making. A diagram is provided below to illustrate how these factors interact:

Tversky was Kahneman's trusted partner, who tragically passed away at a young age, depriving him of the opportunity to share the Nobel Prize with Kahneman for their groundbreaking research. It's worth noting that Tversky, like Kahneman, was an Israeli affiliated with the Hebrew University, where they collaborated closely.


This book offers a comprehensive and stimulating overview. The provided excerpt catalyzes reading, aids comprehension during the reading process, and is a valuable reference afterward. However, it's crucial to emphasize that despite its eloquent and accessible writing style, the book delves into profound and numerous concepts. As a result, it demands reflection within sentences and between them, navigating through examples and ideas.

While the text spans 499 pages, its richness and depth suggest that multiple readings may be worthwhile. The complexity of the content calls for careful consideration, making the book a valuable resource for those seeking a deeper understanding of its subject matter.

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