Influence – The Psychology of Persuasion

Influence by Robert B. Cialdini is an acclaimed book about human tendencies to get persuaded. It shows how marketers use (and sometimes abuse) those psychological traits to get what they want. The reader, on the other hand, can try and armor himself against these methods if he knows about them.

The book is organized around the six guiding principles that Cialdini identifies:

The book is written in a very entertaining style with lots of anecdotes. Cialdini usually annotates his anecdotes with scientific studies exploring the phenomenon at hand, but this book is not really rigorous. Motives are mostly ascribed, not really proven. If you're interested in a more comprehensive and rigorous treatment of psychological processes, I would strongly recommend Daniel Kahnemann's “Thinking, Fast and Slow”.

And counterintuitive experimental results abound: For example, Cialdini cites studies where people let others cut the line to a photocopier more often if those people qualify their request with the zero-information, almost nonsensical clause “because I need to make copies”. The use of the keyword “because” itself signifies to the recipient a reason, even if no such reason is really given.

A nice way to trick customers into buying is by creating a false sense of urgency, with the salesman acting as if he made a mistake with the price that only the customer notices. Buy quickly before he sees his mistake!

This is dishonest, of course, but as opposed to other dishonest tactics there is no gullible victim here, just another malicious person. So it's hard to feel too bad for the customer.

The first important principle shown in the book is the contrast principle: Differences seem exaggerated when the different things are presented one after another. For example, putting your hand into warm water and in cool water after that, makes the cool water seem very cold.

Salesmen can use this principle to their advantage: they will usually try to sell the more expensive item first (a suit), and cheaper accessories afterwards (a belt), because in this order the belt seems to be not a lot of money.


We feel obligated to reciprocate acts of kindness. An example from the book is the practice of the sect of Hare Krishna to “give a gift” to a passerby before asking for a donation. This gift – usually a flower – can be very cheap, even retrieved from the garbage bin and gifted again to the next person, it still greatly increases donations.

The psychological reason is that being indebted feels burdensome. We want to get rid of this obligation. Evolutionary speaking this is a sensible reaction: it fosters cooperation between people.

The interesting part is that this psychological rule works also for uninvited gifts (as the flower), even ones imposed on us after courteously declining. So another person can create a feeling of being obligated towards him. This isn't foolproof and certain, of course, if the mark knows about this effect he can dismiss it. But it's not easy and frictionless, the feeling is still there.

Additionally, we feel obligated to reciprocate, even when the requested favor-in-return is disproportionate. So this can be used to extract value from others, unless they are acutely aware of this, or the requested favor is wildly out of the ballpark.

There is still another way to use this psychological effect to one's advantage: reciprocal concessions. You request something, have this request rejected, and then request something smaller, as if you actually conceded something there.

This second request looks like a real concession, even if it was what you intended to get all along. But now the other person may feel obligated to accept, or at the very least move their counteroffer in your direction.

Again, it's the contrast principle at work: compared to your outlandish first request, the second one seems much more reasonable than it would on its own.

The most beautiful part of this rejection-then-retreat strategy is that sometimes your extreme first request may even be accepted! The potential winnings are enormous. The main disadvantage is that extreme requests may infuriate the other person and make the whole negotiation go sour.

The strategy in selling of starting with the more expensive item mentioned above is also an example of rejection-then-retreat: You start with the top of the line and retreat to some middle-priced item, instead of offering the lowest-priced items immediately. In this way you can extract more value from the buyer on average. “Upselling” is exactly the wrong approach!

The “victims” of this strategy don't even hold resentment (unless you really went too far); studies show that they not only carry out their part of the deal more often than without this strategy, they are even more likely to deal with you in the future!

On the other hand, starting with a small deal is also advantageous, in that it may reel in a much larger deal in the future. This is not contradiction to the “no upselling” part above: “No upselling” applies in a situation where a present customer wants to buy several items. The foot-in-the-door technique applies when the other person is not yet a customer, but you'd like to change that. You relinquish a meaningful profit on your first transaction in order to ensure subsequent transactions with real profits.

The other person being a customer may be important in other regards, as well: for example, in many jurisdictions it is illegal to cold call or write strangers in order to advertise to them. When they are existing customers and a business relationship is in place, it may be legal to advertise to them.

Commitment and Consistency

People are more likely to comply with a larger request after they have already complied with a trivial request. That's even the case when the two requests are only remotely connected. So if you want someone to do something and you feel that there will be resistance, it's best to start with a small request that's unlikely to be declined.

A very interesting anecdote is the one about US prisoners of war in a Chinese prison camp in Korea. The Chinese were regularly running essay-writing contests for the US prisoners. And they were smart enough to let pro-US essays win the contest sometimes, because in that way, prisoners felt they didn't have to betray their country, writing positive things about the US, but still had incentive to slip in a few nods towards the Chinese system, in order to enlarge their chance of winning. So the Chinese got the prisoners on the path to more substantial concessions in their writings.

Another aspect was that the prizes for winning the contest were low, a fruit here, a few cigarettes there. The writers had to “own” what they were writing, there couldn't be any doubt it might only have been written just for a big prize.

When people own what they have written themselves, they identify with it and it's hard to change their stance later. This can be handy in more benign circumstances: a salesman that lets the buyer fill out the sales agreement will find that there will be fewer cancellations. People feel more bound by a contract when they have physically written part of it.

The same applies to testimonial contests that many companies run. At first glance it seems strange that pretty substantial prizes are offered for a postitive line or two about their product, but those testimonials (by real, common people) can not only be used in advertising, they change the writer's perception about the product and cement this opinion.

Cialdini suggests that jury forepersons stick to secret balloting in the jury room, because when done this way no juror feels constrained by their need for consistency. Changing your opinion is easier when you haven't visibly committed to it. This should result in fewer hung juries.

Is there a way to resist this psychological need for consistency? Of course, it is easier when you're aware of the effect. But the effect is only lessened and must actively be overcome by the rational mind, there's no way to really switch it off.

Should this need for consistency be overridden? Most of the time: no. It is a good trait to stick to your convictions most of the time. There are two broad categories of situations where it's probably better not to be consistent. First, when your gut is telling you that you've been trapped. You don't really want to do something, but feel an obligation. And second when knowing what you know now your first reaction tells you that you wouldn't do it again. In those cases it's probably best to break consistency.

Social proof

A good example for social proof (albeit a sad one) is so-called witness apathy. Quite often when something bad happens and a person needs immediate help, there are many bystanders, but nobody is helping.

The reason is that few emergencies are totally obvious to the onlooker. And while he ponders if it is indeed an emergency and he should get involved (it would be embarassing if he acted without any need for it), he sees all those other people standing around him. None of them helping. So it seems to be consensus opinion that no help is needed. Unfortunately help is needed, very much so, but everyone standing around is going through the exact same thought process. So it's actually more probable for people to render assistance when fewer people are around. Or even only one. That one cannot possibly convince himself that others would help if there was the need. But as soon as one person helps, others participate. Helping is infectious. It is now “socially safe” to do so.


Not surprisingly, people tend to obey (perceived) figures of authority. In the Milgram experiment the participants continued to give (ostensible) electric shocks despite very strong signs that the experiment has gone too far, just because the supervisor in the lab coat told them so.


Again, it's common sense that you try to help people more when you like them. But how is liking influenced?

First, physical attractiveness helps. You may not be looking for a life partner, but the attractive person (even of the same gender) has an advantage when it comes to you liking them.

Also, similarity is a big factor. You're both playing golf? You're both in academia? You both like to travel to the Canary Islands? You're positively predisposed towards one another.

We like things that are familiar to us. An interesting experiment is taking a photo of your face and producing two versions of it: the original and one, where left and right have been swapped. Your friends will probably like the original more, while you prefer the swapped one. The reason is simple: you know your face mostly from looking into a mirror.

Some situations make us more receptible to ideas, we are more favorable towards ab issue when it is presented while we eat.

It's very hard to avoid this liking effect, we can only recognize it and then force ourselves to separate the issue from the person.


Why do people usually interrupt a conversation when their phone rings, even if they don't expect an important call? The other person in the conversation is still going to be there a minute later. The caller might be unreachable later.

We feel a lot of pressure when we're made to believe that an opportunity would be lost a short time later. Therefore all those sales with time limits and offers only valid today. We feel we might miss out on some great deal.

Marketers use this all the time. They also like to feign small inventory, so you should really get this item now.

But it gets really devastating when (perceived) scarcity meets rivalry. Only one car on sale, but there are two other people interested in it, and willing to buy immediately. Salesmen like to have several prospective buyers show up at the same time. So they schedule them at the same time.

Usually in those situations we go astray. We don't really want to enjoy, or use the scarce item. We want to possess it. Buyer beware!


It's not just the flesh that is weak. The mind is just as weak, or at least malleable. We cannot switch off our evolutionary baggage and programming, but we can be aware of it and keep it at bay. In Daniel Kahnemann's parlance: we can activate System 2 to override System 1.

Influence is eye-opening, entertaining and gracefully short. It doesn't climb to such intellectual heights as Kahnemann's book, but it's a very good read.