Influence Summary
The Key Ideas, What Holds Up, and How to Use Them

Influence is a classic book about why people say yes. Here are its big ideas in our own words, a check of its best-known studies and stories against later research, and a few small practices drawn from the parts that hold up.

About the book

Influence is by Robert B. Cialdini, Regents’ Professor Emeritus of Psychology and Marketing at Arizona State University. William Morrow first published it in 1984 as Influence: How and Why People Agree to Things; the 1993 edition carried the subtitle The Psychology of Persuasion, and a textbook version, Influence: Science and Practice, has been published alongside it. The 2021 New and Expanded edition adds a seventh principle, unity. It is written for general readers and mixes experiments with everyday examples. In the author’s own description of the 2021 edition, it shows how the principles work and how to defend yourself against unethical influence attempts.

We did not read the full book. We read short passages of the 1984 and 1993 printings, and of the textbook edition, through the Internet Archive’s search-inside tool, the author’s own descriptions of the principles and of the 2021 edition, and the studies behind the claims. We could not open the 2021 edition, so the unity chapter is described only from the author’s summary.

The big ideas

1. We run on shortcuts

Cialdini’s starting point is that people often respond to a single cue instead of weighing all the information, much as some animals react to one trigger. He calls these automatic responses “click, whirr”. An early example in the book is a 1978 study in which a stranger asked to jump the queue at a photocopier, and giving a reason, even an empty one, made a large difference when the favour was small.

2. Reciprocity

People feel obliged to give back what they have received first: a gift, a favour, a concession. One tactic the book describes is what it calls the rejection-then-retreat technique, better known as the door in the face: ask for something large, and when it is turned down, retreat to the smaller thing you wanted, which feels like a concession to be repaid.

3. Commitment and consistency

Once people have taken a stand, they tend to act in line with it. The book’s examples include the foot in the door, where agreeing to a small request makes a later, larger one easier to accept, and the low-ball, where a deal agreed at one price tends to survive a small increase in the cost.

4. Social proof

When unsure what to do, people look at what others like them are doing. Cialdini and colleagues later tested this with hotel signs telling guests that most other guests reused their towels. The book also uses the 1964 killing of Catherine (Kitty) Genovese to explain why a crowd of onlookers can fail to help.

5. Liking

People say yes more readily to those they like, and the author’s own summary names three causes of liking: similarity, compliments, and working together towards shared goals. In one 2004 paper, people who believed they shared a birthday, a first name or a fingerprint type with a requester were more likely to grant the request.

6. Authority

People tend to follow credible, knowledgeable experts, and outward signs of authority, such as titles and clothing, can sway people too. The book discusses Stanley Milgram’s obedience experiments over several pages.

7. Scarcity

People want more of what they can have less of. The author’s own example is the rush to buy seats on Concorde after British Airways announced in 2003 that it would stop the twice-daily London to New York flight.

8. Unity

New in the 2021 edition. Announcing it, Cialdini wrote that people are inclined to favour someone who shares a significant social identity, “someone they consider one of them”, and that its power comes from shared identities such as family, nationality or religion rather than shared tastes. We could not read the chapter itself.

What holds up

The broad picture holds: people do take mental shortcuts, and several of the techniques work in controlled tests. But the size of the effects is often smaller than the book’s stories suggest, a few famous examples have not held up well, and one, the 38 silent witnesses, is not supported by the evidence. The rows below give each claim, the verdict and the source.

How to use it

These practices come only from the parts that hold up, or partly hold up. They describe; what fits your situation is your call.

1. Reading a deal at its final cost. The low-ball held up in a meta-analysis, and it works best after a public first agreement. Looking again at the full price, once the extras appear, is a way to notice when the cost has moved after you said yes.
2. Asking whether you wanted it before you saw it was scarce. Scarcity cues raise how much people say they want something. A pause to ask whether the item was wanted before the countdown or the “only 3 left” appeared separates the thing from the pressure.
3. Separating saying yes from doing it. The door in the face moves spoken agreement more than it moves what people then do. A request agreed to on the spot after a bigger one was refused can be worth a second look later.
4. Giving the real reason. In Langer’s study, when the favour was large, the empty reason did no better than none (24% each), while the real reason got 42%, a gap the authors reported only as a trend in groups of about 25. Explaining why you are asking is the one version of the “because” effect that did not fall flat when the favour grew.
5. Checking whether the authority is an authority on this. Milgram’s obedience findings partly held up, and how many obeyed depended heavily on the set-up. Asking what the person knows about this particular question, and what they gain from your answer, is a quick check.

Who it’s for, and who can skip it

It suits readers who want a lively, story-led tour of persuasion, and anyone who wants to recognise the tactics used on them in shops, sales calls and fundraising. Readers who want effect sizes and replication status will need to look past it to the later research, since several of its best-known studies are smaller or shakier than the stories make them sound. Readers who already know the six principles from courses or summaries will find little new in the core ideas.

If you liked this

• How to Win Friends and Influence People, summarised, the older, story-based book on the same subject, with its own techniques checked.
• Cognitive biases checked, which looks at the bystander effect and other famous findings.
• Thinking, Fast and Slow, summarised, on the mental shortcuts behind many of these effects.

Sources

• R. B. Cialdini, Influence: How and Why People Agree to Things (William Morrow, 1984) and Influence: The Psychology of Persuasion (William Morrow, 1993), read as search-inside snippets of the Internet Archive copies (1984, 1993); Influence: Science and Practice, 5th edition (Pearson, 2009), snippets.
• Influence at Work, “About Dr. Cialdini”, “Principles of persuasion” and the books page (2021 edition).
• J. M. Burger, “The foot-in-the-door compliance procedure: a multiple-process analysis and review”, Personality and Social Psychology Review 3 (1999); M. Gamian-Wilk and D. Dolinski, “The foot-in-the-door phenomenon 40 and 50 years later”, Psychological Reports 123 (2020).
• R. B. Cialdini et al., “Reciprocal concessions procedure for inducing compliance: the door-in-the-face technique”, Journal of Personality and Social Psychology 31 (1975); T. H. Feeley, A. E. Anker and A. M. Aloe, “The door-in-the-face persuasive message strategy: a meta-analysis of the first 35 years”, Communication Monographs 79 (2012); O. Genschow et al., “Does social psychology persist over half a century? A direct replication of Cialdini et al.’s (1975) classic door-in-the-face technique”, Journal of Personality and Social Psychology 120 (2021); T. H. Feeley, “50-year review of the door-in-the-face message strategy”, Communication Monographs (online 16 December 2025).
• J. M. Burger and D. Caputo, “The low-ball compliance procedure: a meta-analysis”, Social Influence 10 (2015).
• N. J. Goldstein, R. B. Cialdini and V. Griskevicius, “A room with a viewpoint”, Journal of Consumer Research 35 (2008); G. Bohner and L. E. Schlüter, “A room with a viewpoint revisited”, PLoS ONE 9 (2014); B. Scheibehenne, T. Jamil and E.-J. Wagenmakers, “Bayesian evidence synthesis can reconcile seemingly inconsistent results”, Psychological Science 27 (2016); B. Scheibehenne, Q. F. Gronau, T. Jamil and E.-J. Wagenmakers, “Fixed or random? A resolution through model averaging”, Psychological Science 28 (2017); G. Reese, K. Loew and G. Steffgen, “A towel less: social norms enhance pro-environmental behavior in hotels”, Journal of Social Psychology 154 (2014).
• R. B. Cialdini, “This should be labeled a universal principle of influence”, Psychology Today, 5 April 2021.
• R. Manning, M. Levine and A. Collins, “The Kitty Genovese murder and the social psychology of helping”, American Psychologist 62 (2007); R. D. McFadden, “Winston Moseley, 81, killer of Kitty Genovese, dies in prison”, The New York Times, 4 April 2016 (archived); P. Fischer et al., “The bystander-effect: a meta-analytic review”, Psychological Bulletin 137 (2011).
• E. Langer, A. Blank and B. Chanowitz, “The mindlessness of ostensibly thoughtful action”, Journal of Personality and Social Psychology 36 (1978); V. S. Folkes, “Mindlessness or mindfulness: a partial replication and extension”, Journal of Personality and Social Psychology 48 (1985); M. S. Key, J. E. Edlund, B. J. Sagarin and G. Y. Bizer, “Individual differences in susceptibility to mindlessness”, Personality and Individual Differences 46 (2009).
• S. Milgram, “Behavioral study of obedience”, Journal of Abnormal and Social Psychology 67 (1963); J. M. Burger, “Replicating Milgram: would people still obey today?”, American Psychologist 64 (2009); S. A. Haslam, S. D. Reicher, K. Millard and R. McDonald, “‘Happy to have been of service’”, British Journal of Social Psychology 54 (2015); G. Perry, A. Brannigan, R. A. Wanner and H. Stam, “Credibility and incredulity in Milgram’s obedience experiments”, Social Psychology Quarterly 83 (2020); N. Haslam, S. Loughnan and G. Perry, “Meta-Milgram: an empirical synthesis of the obedience experiments”, PLoS ONE 9 (2014).
• S. Worchel, J. Lee and A. Adewole, “Effects of supply and demand on ratings of object value”, Journal of Personality and Social Psychology 32 (1975); B. Barton, N. Zlatevska and H. Oppewal, “Scarcity tactics in marketing: a meta-analysis of product scarcity effects on consumer purchase intentions”, Journal of Retailing 98 (2022).
• J. M. Burger et al., “What a coincidence! The effects of incidental similarity on compliance”, Personality and Social Psychology Bulletin 30 (2004).

Checked October 2026. What we read: short search-inside passages of the 1984 and 1993 printings and of the 2009 textbook edition (not the full text of any edition, and not the 2021 edition); the author’s own pages on his principles and books; the full texts of the 2016 towel re-analysis and its 2017 reply, the 1978 photocopier study and the 1985 replication; the 2016 New York Times obituary (archived copy); and the abstracts of the other studies listed above.