Influence

We feel obliged to repay what we have been given. The rule appears in every human society studied, for good reason: it allowed the division of labour and systems of aid, because a person could give something away without actually losing it. Because it is universal and trained into us from childhood, indebtedness is genuinely uncomfortable to carry - and people will do a good deal to discharge it.

Three exploitable features:

• It is overpowering. An uninvited favour still creates obligation. In Dennis Regan's experiment, a stranger who bought someone an unrequested soft drink could afterwards sell them substantially more raffle tickets - and whether the subject liked the stranger stopped mattering. The obligation overrode the preference.
• It triggers uneven exchanges. Because indebtedness is unpleasant and refusing a gift is awkward, a small unsolicited favour can produce a much larger return. The Hare Krishna flower, pressed into the hand of a traveller who did not want it and could not give it back, funded temples.
• It applies to concessions. The one most people have not thought about. Retreat from a large request to a smaller one and the other person feels obliged to reciprocate your concession by moving toward you. This is rejection-then-retreat, or door-in-the-face: students asked to chaperone delinquents on a zoo trip agreed at about 17% when asked directly, and about 50% when the request followed a refused request to counsel delinquents for two years. It also produces greater satisfaction and follow-through, because the target feels responsible for the final deal.

Once we have taken a stand, we encounter pressure to behave consistently with it. Consistency is socially valued, often genuinely adaptive, and offers a shortcut through complexity: once a position is fixed you no longer have to think about the question. That last benefit is also the danger - it is a very comfortable place to hide from evidence.

The lever is commitment. Freedman and Fraser's study: homeowners asked to allow a large, badly lettered DRIVE CAREFULLY billboard on their lawn agreed at about 17%. Among those who two weeks earlier had agreed to display a three-inch safe-driving sign, over 76% agreed. The tiny first step had changed how they saw themselves.

Four features make a commitment stick:

• Active rather than passive - the person does something, not merely agrees
• Public - we are far more consistent with positions others witnessed
• Effortful - we value what we have suffered for, which is his account of initiation rituals and hazing
• Internally chosen - a commitment made under obvious external pressure produces no change in self-image at all

He draws the parenting conclusion explicitly: threats and bribes produce compliance while present, and no lasting change once removed.

Two field tactics follow: the written commitment (testimonial contests requiring an essay beginning "why I like this product"), and the lowball - a good offer secures the decision, then the offer is worsened after the person has begun generating their own reasons for the choice. Cialdini watched this taught directly in car dealerships.

We determine what is correct by finding out what other people think is correct. Usually a sound heuristic - crowds are often right, and it saves enormous independent investigation. The failures come in two identifiable conditions.

Uncertainty. When a situation is ambiguous we look to others, and if everyone is looking at everyone else the group settles into a stable inaction nobody chose. This is pluralistic ignorance, and it underlies the bystander effect: more witnesses, less likely help - partly diffused responsibility, partly everyone reading everyone else's outward calm as evidence nothing is wrong.

Similarity. We are most influenced by people we perceive as like ourselves. Cialdini cites David Phillips's work on the Werther effect, finding detectable increases in suicides and in single-occupant crashes following widely publicised suicides, tracking the demographics of the reported case.

The tactics are everywhere once you see them: canned laughter, which people reliably say they dislike and which reliably works; the salted tip jar; the queue outside the club; testimonials from ordinary-looking people rather than experts; and "fastest growing", which is a claim about other people's behaviour rather than about the product.

We prefer to say yes to people we like. Obvious in principle; the value of the chapter is that Cialdini itemises what produces liking, because each item is manufacturable.

• Physical attractiveness, producing a halo effect - attractive people judged more talented, kinder, more honest, more intelligent. Almost nobody believes this affects them.
• Similarity, in almost any dimension: opinions, background, dress, even a shared name or birthplace. Salespeople are trained to find one and mention it.
• Compliments, which work with startling reliability even when transparently insincere and even when the motive is obvious.
• Contact and familiarity - but only when the contact is pleasant. Contact under competitive or unpleasant conditions makes things worse, which is why desegregating schools alone did not reduce prejudice, and cooperation toward a shared goal did (the jigsaw classroom).
• Association, the deepest of the five. The weather forecaster blamed for the weather; doing business over lunch so the proposal is associated with the food; and basking in reflected glory, where fans say we won and they lost about a team they have never played for.

We are trained from birth that obedience to legitimate authority is correct, and the training goes very deep.

Cialdini opens with Stanley Milgram's obedience experiments, in which ordinary volunteers instructed by a researcher in a lab coat appeared to deliver escalating and eventually dangerous shocks to a protesting stranger. Roughly two-thirds went to the maximum; psychiatrists asked to predict beforehand had estimated about one in a thousand.

The detail that makes this relevant to persuasion rather than merely to atrocity: the researcher had no power over the participants at all. He could not punish, pay or fire them. He simply appeared to be the authority in the room.

Which leads to the practical warning. Because we respond automatically, we respond to the symbols of authority rather than the substance - and symbols can be worn by anyone:

• Titles, the easiest to claim, and which measurably alter how people perceive the same person's height and status
• Clothing - a man in a business suit gets substantially more compliance jaywalking than the same man dressed casually; a uniform more still
• Trappings - cars, offices, jewellery, the visible apparatus of position

His most alarming example is from healthcare: researchers telephoned hospital wards posing as a physician and instructed nurses to give an obviously excessive dose of an unauthorised drug; the great majority began to comply before being stopped. He pairs it with a prescription written "place in R ear", which a nurse and patient jointly interpreted as an instruction to put ear drops in the patient's rectum, neither pausing to ask whether that made sense.

Opportunities seem more valuable when their availability is limited. Two reasons: difficulty of acquisition is usually a decent proxy for quality, and - doing most of the work - as things become less available we lose freedom, and we hate losing freedoms we already have. That is psychological reactance.

Reactance shows up early. The terrible twos are a child's first sustained encounter with the discovery that their freedoms are limited. It explains the Romeo and Juliet effect, where parental interference intensifies a young relationship. And it explains something politically important: censorship reliably increases desire for the censored material, and in some studies makes people more sympathetic to the banned position without having read it. Cialdini's advice to anyone with information they cannot suppress is that suppression is the strongest possible endorsement.

Two amplifiers:

• Newly experienced scarcity beats constant scarcity. Something that has just become restricted is far more desirable than something always rare. He notes this is why periods of improving conditions followed by sudden reversal are historically associated with revolution, rather than periods of unrelieved deprivation.
• Competition. Scarcity plus visible rivals produces something close to frenzy - the mechanic of the auction, the queue, and the property open house scheduled so all the buyers arrive at once.

Added in the 2021 edition, and Cialdini argues it is distinct from liking rather than a variant of it.

Liking is about people who are similar to us. Unity is about people we consider to be part of us. The question is not do we resemble one another but are we of the same thing - family and kinship, place of origin, ethnicity, or membership of a group where the individual and the group are experienced as overlapping.

Two categories create it:

• Being together - kinship, and the surprisingly strong effects of shared locality. The language of family used outside the family ("we're like family here") works because it borrows the response due to actual kin.
• Acting together - synchronous and coordinated activity (marching, singing, moving in time) measurably increases cooperation and mutual liking, including in experiments with young children. And co-creation: when people build something together the bond is much stronger than when one party receives the other's work. Cialdini notes that asking someone for advice, rather than their opinion, invites a co-creative posture and reliably increases their subsequent commitment.

Unity is the most obviously double-edged principle, since the mechanism that produces solidarity within a group produces indifference or hostility toward those outside it - and Cialdini is more explicit about the ethical hazard here than anywhere else in the book.