Can doctors and investment advisers be trusted? And do we live more for experiences or memories? In a SPIEGEL interview, Nobel Prize-winning psychologist Daniel Kahneman discusses the innate weakness of human thought, deceptive memories and the misleading power of intuition.

SPIEGEL: Professor Kahneman, you’ve spent your entire professional life studying the snares in which human thought can become entrapped. For example, in your book, you describe how easy it is to increase a person’s willingness to contribute money to the coffee fund.

Kahneman: You just have to make sure that the right picture is hanging above the cash box. If a pair of eyes is looking back at them from the wall, people will contribute twice as much as they do when the picture shows flowers. People who feel observed behave more morally.

SPIEGEL: And this also works if we don’t even pay attention to the photo on the wall?

Kahneman: All the more if you don’t notice it. The phenomenon is called “priming”: We aren’t aware that we have perceived a certain stimulus, but it can be proved that we still respond to it.

SPIEGEL: People in advertising will like that.

Kahneman: Of course, that’s where priming is in widespread use. An attractive woman in an ad automatically directs your attention to the name of the product. When you encounter it in the shop later on, it will already seem familiar to you.

SPIEGEL: Isn’t erotic association much more important?

Kahneman: Of course, there are other mechanisms of advertising that also act on the subconscious. But the main effect is simply that a name we see in a shop looks familiar — because, when it looks familiar, it looks good. There is a very good evolutionary explanation for that: If I encounter something many times, and it hasn’t eaten me yet, then I’m safe. Familiarity is a safety signal. That’s why we like what we know.

SPIEGEL: Can these insights also be applied to politics?

Kahneman: Of course. For example, one can show that anything that reminds people of their mortality makes them more obedient.

SPIEGEL: Like the cross above the altar?

Kahneman: Yes, there is even a theory that deals with the fear of death; it’s called “Terror Management Theory.” You can influence people by just reminding them of something — it can be death; it can be money. Any symbol that is associated with money, even if it’s just dollar signs as a screensaver, ensures that people will pay more attention to their own interests than they will want to help others.

SPIEGEL: It seems that priming works primarily in favor of the political right.

Kahneman: It would work just as well the other way around. There’s an experiment, for example, in which people were playing a game but, in the first group, it was called a “competition game” and, in the other group, it was called a “community game.” And, in the latter case, people acted less selfish even though it’s exactly the same game.

SPIEGEL: Is there no way to escape those powerful suggestions?

Kahneman: It isn’t easy, at any rate. The problem is that we usually don’t notice these influences.

SPIEGEL: That’s pretty unsettling.

Kahneman: Well, it can’t be too bad because we live with that all the time. That’s just the way it is.

SPIEGEL: But we want to know what our decisions are based on!

Kahneman: I’m not even sure I want that, to be honest, because it would be too complicated. I don’t think we really are very keen to be self-controlled all the time.

SPIEGEL: You say in your book that, in such cases, we leave the decisions up to “System 1.”

Kahneman: Yes. Psychologists distinguish between a “System 1” and a “System 2,” which control our actions. System 1 represents what we may call intuition. It tirelessly provides us with quick impressions, intentions and feelings. System 2, on the other hand, represents reason, self-control and intelligence.

SPIEGEL: In other words, our conscious self?

Kahneman: Yes. System 2 is the one who believes that it’s making the decisions. But in reality, most of the time, System 1 is acting on its own, without your being aware of it. It’s System 1 that decides whether you like a person, which thoughts or associations come to mind, and what you feel about something. All of this happens automatically. You can’t help it, and yet you often base your decisions on it.

SPIEGEL: And this System 1 never sleeps?

Kahneman: That’s right. System 1 can never be switched off. You can’t stop it from doing its thing. System 2, on the other hand, is lazy and only becomes active when necessary. Slow, deliberate thinking is hard work. It consumes chemical resources in the brain, and people usually don’t like that. It’s accompanied by physical arousal, increasing heart rate and blood pressure, activated sweat glands and dilated pupils …

SPIEGEL: … which you discovered as a useful tool for your research.

Kahneman: Yes. The pupil normally fluctuates in size, mostly depending on incoming light. But, when you give someone a mental task, it widens and remains surprisingly stable — a strange circumstance that proved to be very useful to us. In fact, the pupils reflect the extent of mental effort in an incredibly precise way. I have never done any work in which the measurement is so precise.

(Editor’s note: Read on. Very fascinating. His book, “Thinking, Fast and Slow” is good too.)