Book Notes #004 - Influence: The Psychology of Persuasion by Robert B. Cialdini, PH.D.

Updated: Feb 25


Rating: 4.0/5 ⭐️

Topic: Non-Fiction (psychology, influence, and persuasion)

Main ideas/information - Good.

The main ideas discussed in this book are great concepts to learn more about. I believe that everyone should be aware of the cognitive biases the human mind possesses and their power to influence our behavior.

Examples & stories - Okay.

The stories and examples used in this book are okay. Some are research studies, others are newspaper articles and very few are personal stories.

Engagement - Medium.

The book's main focus on how cognitive biases are used by con artists, cult leaders, and unethical salespeople are far too many. This emphasis on the negative makes it hard to keep reading and remain engaged.

Overall Rating - 4.0/5 ⭐️

Overall, this is a good book to read if you want to learn more about what cognitive biases are and how they influence our behavior. I would recommend skimming through the chapters and only taking the main information of the chapters.



“A well-known principle of human behavior says that when we ask someone to do us a favor we will be more successful if we provide a reason. People simply like to have reasons for what they do.


The main idea of the book is to discuss the six "weapons of influence" otherwise known as cognitive biases. Cognitive biases are automatic responses to behavior based on stereotyping. The reason we have cognitive biases is that most of the time is easier and more efficient to make faster decisions that are based on assumptions to save us time and energy.

Ex. The wine testing experiment - The Contrast Principle.

There was an experiment conducted where people were told that they were testing two different wines. One was more expensive than the other, the most expensive wine was rated "better" than the cheaper option, but in fact, both wines were the same!

This cognitive bias is known as the contrast principle, where "Price = Quality". Making this assumption, save us time and energy.


The rule of reciprocation states that "we should try to repay, in kind, what another person has provided us". This rule talks about how humans have evolved with the idea of sharing and honoring reciprocity in our actions.

There is a strong cultural pressure to be "fair" and so the rule of reciprocity has been used as a marketing technique.

Have you ever wondered why you are receiving free samples?

By giving away free samples or "gifts", some people feel the need to then buy the product in exchange. Gifts are initial transactions to envoke the reciprocity rule. It may not always work but depending on your personality the impact of this bias might be stronger.


This rule is based on "our nearly obsessive desire to be (and to appear) consistent with what we have already done".

Has it ever happened to you that you commit to buy something, and in the middle of it you end up regretting the purchase because you saw there is a better option and ended up justifying your actions?

The reason this is a powerful bias is that consistency is seen as a good trait to have in our society. On the other hand, changing our decisions last minute and acting unpredictably is seen as a less desirable trait. People like to predict other people's behavior so we are afraid to change our minds once we have made it public.


The principle of social proof, states that one way to find out what is "correct" is to look at what other people think is correct.

This principle can be seen in the world of online buying. In the uncertainty of choosing to buy something online, people rely on testimonials and reviews. One best way to create trust is to provide social proof. That's why amazon emphasizes you leaving a review on each purchase as a way to help others make a better decision.


As a rule, we prefer to say "yes" to a request from someone we know and like. Two main biases are being played here.

  • Physical attractiveness: "Research shows that we tend to associate physical attractiveness to traits such as talent, kindness, honesty, and intelligence". Think about celebrities, tv hosts, influencers, public figures, etc. We are most likely to like and trust someone based on their physical appearance.

  • Similarity: On the other hand, we also like people that look like us and/or share backgrounds and interests similar to us. Familiarity creates trust.


We have a cognitive bias towards obeying authority and there are ways we can assume someone has it.

  • Titles: CEO, Ph.D., MANAGER, etc.

  • Clothes: Hospital white, police blue, army green, etc. (it's illegal to impersonate any of this by the way)

  • Trappings: Jewelry, cars, exotic things, etc.

Con artists, for example, hide underneath their titles, clothes, and trappings of authority, to influence people's behavior. In a lighter view, dressing more formally can make you look more trustworthy in a job interview or networking event.


Probably the most straightforward use of the scarcity principle occurs in the "limited number" tactics when the customer is informed that a certain product is in short supply.

Think about serial numbers. If there is a limited amount of something, by default the value will go up. That's how art can become more valuable with time because there are only a fixed number of painting a famous artist can produce in their lifetime. And even more, once the artist has passed away, think about Leonardo da Vinci paintings.

(Side note; Leonardo da Vinci's total output in painting is rather small; there are less than 20 surviving paintings) - Britannica


  1. Contrast Principle.

  2. Commitment and consistency.

  3. Reciprocity rule.

  4. Social proof.

  5. Liking.

  6. Scarcity.

Thanks for reading! We want to know what did you think about this week's books notes? Have you read this book? What were your thoughts?