Predictably Irrational

Predictably Irrational: The Forces that Shape Our Decisions
Author: Dan Ariely


This book is about the systematic and predictable irrationality that plagues human decision-making and affects all our activities (page xxx). The author, who admits to ‘an unusual way of looking at the world’, explores the innumerable ways people make decisions without properly considering all the options, and he explains why people make choices without regard for their long-term consequences. The book illustrates how people make senseless decisions because of an aversion to thinking, an activity the author says is ‘hard and sometimes unpleasant’ (page 3).

Thinking. Creative Ignition on Flikr.

One of the major reasons the book identifies as a cause for irrational decision-making is impulsive behaviour. The author cites research, many his own, which clearly show that people make risky decisions because they overestimate how much self-control they will have when they are in a state of arousal (pages 89-90). These studies illustrate how this hot state and consistently overrides our morality and good judgment, and how it triggers many irrational acts such as procrastination, dangerous driving, and sexual indiscretions (pages 97-104). It appears that people fall prey to temptation because they are unable to recognise the limits of their self-control in emotionally charged situations (page 116).

Temtation. Vincent Luigi Molini on Flikr.

The author addresses the significant impact irrational decisions make in commerce. As an example, he explains why buyers are significantly influenced, when they bargain, by the initial price the seller sets. He details the nature of this type of anchoring with reference to the studies of Uri Simonsohn and George Lowenstein on ‘arbitrary coherence‘ (page 30). The author also discusses the human tendency to rely on comparisons when making choices, and how this ‘relativity‘ determines many commercial decisions (page 4). This, for example, explains why buyers always favour the second most expensive option, an observation which marketers use to manipulate customers to buy their favoured products (page 9). The book explores other irrational human behaviours such as why people act generously within social norms, but stringently in market norms, and why people are willing to work harder for a cause than they would for money (pages 71-73).

Apples & Oranges-They Don’t Compare. Michael Johnson on Flikr.

One of the most interesting subjects the book explored is human dishonesty. The author shows how, ‘given the opportunity, many honest people will cheat… but they cheated just a bit’ (page 201). This characteristic nature of human cheating appears to be universal, and extends to professional dishonesty such as when doctors ‘do unnecessary surgeries and other procedures just to boost the bottom line’ (pages 210-211). Other forms of irrational behaviour which the book covers are more subtle, such as the subconscious power of the placebo effect; the author illustrated this with the study by orthopaedic surgeon J. B. Moseley, who first demonstrated that both real and sham arthroscopic surgery had the same effect on patients (pages 174-175). Another subtle irrationality is people’s incomprehensible desire to keep all their options open, even if this is ultimately to their disadvantage (page 142). The book reviewed many other psychological influences driving irrational decision-making such as herding (page 36), the endowment effect (pages 133-134), and the power of ‘free‘ (page 60).

A Cheating Oldie but Goodie. Jared Stein on Flikr.

The book is replete with stories which the author used to support his arguments. An example is the interesting anecdote of Xiang Yu, the Chinese commander who ordered his troops to burn their ships. He took this decision to make it clear to his army that retreat was not an option for them in the battle they were about to fight (pages 139-142).

Choices. Derek Bruff on Flikr.

The author offered many solutions to enable people to overcome their irrational behaviour. He says ‘although irrationality is commonplace, it does not necessarily mean we are helpless’. He advises people to avoid rather than attempt to overcome temptation, and to use moral benchmarks to minimise dishonest behaviour (page 209). The book urged people to be vigilant in circumstances which impair decision-making; to force themselves to think differently about their decisions; and to use technology to overcome their cognitive shortcomings (page 244). Other tips include the use of restrictive deadlines and pre-commitments to overcome procrastination (pages 101-116).

The Essence of Vigilance. phil Dolby on Flikr.


This is an excellent book with several key insights into human behaviour. The author’s writing style is very informal, and the underpinning research is clearly described. There were however some shortcomings, such as the unnecessarily details of how the author became involved in behavioural economics. The expanded section of the book also contained many unnecessary and unhelpful reflections and comments, which readers can conveniently ignore. The author also had an irritating style of interrupting a flow of a subject, often going off to describe a possibly related item, before returning to resume the topic. These aside, the book makes a significant contribution to the understanding of the factors that impair decision-making.

Overall assessment

Understanding the irrational underpinnings of decision making is key to health care, both at the frontline and at board level. The book offers invaluable insights into human behaviour to guide the caregiver and their patients, and I highly recommend it to all doctors.

Book details

  • Publisher, Place, Year: Harper, London, 2008
  • Number of chapters: 13
  • Number of pages: 368
  • ISBN: 978-0-00-725653-2
  • Star rating:
  • Price: £6.29

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