Feb 19, 2014: Happy Anniversary

February 19, 2014 BY danariely

Six years ago, an orange-and-blue book was first set free into the world. It was the beginning of an amazing journey — not only for the book, but also for me. This book traveled to all parts of the world, translated into ~40 different languages, and I traveled with it. To this day, I still find myself in the far regions of the earth, meeting new people, having interesting conversations, and understanding the world in a different way.

As I reflect today on these last six years, what is amazing to me is the degree to which this book was a starting point for the rest of my life. And the journey continues.

Happy Anniversary,


Predictably Irrational App for iPad and iPhone

June 5, 2013 BY danariely

Thanks for downloading the PI app — you’ve brought it up to the #2 spot in iTunes!!

If you’d like to give the app a review in the app store, I’d very much appreciate it.


Ask Ariely: On Chips and Dips, Expectations, and Gossip

January 19, 2013 BY danariely

Here’s my Q&A column from the WSJ this week — and if you have any questions for me, just email them to AskAriely@wsj.com.


Dear Dan,

While I’m watching sports, I often find myself with the same problem. I will have too many chips for my dip, but if I open up another can of dip I’ll have too much dip for my chips. I don’t want the extra can of dip to go to waste, but I don’t want to have to eat dry chips. What should I do?


This is indeed an important problem! What you are experiencing is a problem with ending rules. The chips and dip each provide an experience for you that ends at a different time, making it hard to figure out when to stop.

One solution would be to convince the chip and dip manufacturers to bundle packages that complement each other in terms of size. Another approach would involve pacing yourself from the get-go in terms of the chip-to-dip ratio. A third idea would be to invite a friend who only likes chips (or dislikes the dip you have).

More seriously, the problem you are describing is part of a more general issue, as Brian Wansink shows in his wonderful book “Mindless Eating: Why We Eat More Than We Think.” We don’t stop eating when we have had a sufficient amount of food, but when we’ve finished everything on the plate. The best approach may be to think about how much chips-and-dip you want to consume, transfer that amount to small dishes, and stop making decisions based on the size of the packaging.


Dear Dan,

In “Predictably Irrational,” you wrote about the “Effect of Expectations,” and you demonstrated that we are prone to perceiving things as being more like what we expect them to be than as what they actually are. As an example, you showed that we would experience a glass of wine as better if we had seen positive reviews of it before tasting it. Well, these findings mostly fit with my own experience; however, what you didn’t mention is the possibility of a negative effect for expectations that are too good. In other words, is the effect the same when something is extremely overhyped?

My own observation is that when I passionately recommend a movie to my friends, sometimes their feedback is: “It wasn’t that good. I thought it would be really amazing.” I suspect that they’re experiencing a negative feeling toward the movie because I over-hyped it. Do you think that overhyped expectations can backfire?

—Omid Sani

My intuition is basically the same as yours. When I overhype something, I also feel like people end up with very high expectations (that is, assuming they trust my opinion) and that this can decrease their enjoyment of the experience.

Here is how I view the issue: Heightened expectations can change our experience by (let’s say) 20%, which means that as long as the increased expectations are within this range, the expectation can “pull” the experience and influence it. But when expectations are too extreme (let’s say 60% heightened), the gap with reality becomes too wide, and they may backfire and reduce enjoyment.

If you want your friends to experience something as better than it truly is, go for it and exaggerate. But don’t exaggerate by too much. This kind of “fudge zone” also suggests that in areas of life where people are not experts, you can exaggerate a bit more.


Dear Dan,

I’m at a loss for understanding the popularity of gossip newspapers and magazines? What is the attraction??


I don’t understand it myself, but I suspect that some of the attraction has to do with social coordination.

I have never been in a discussion where people said “I only wish we had more time to talk about the weather / sports / gossip.” But, given the need to find common topics for discussion, these are some of the easiest common denominators to find.

See the original article in the Wall Street Journal here.

The paperback version of PI is out…

April 27, 2010 BY danariely

As of today the paperback version of PI is out.

I took out the parts about the stock market, and added 2 new chapters: one about the effects of social norms, and one about the cycle distrust in marketers and markets.

Sadly I cannot distribute these digitally, but if you are every in a book store or a library (or if you think that this worth $10) ….

Irrationally yours


Announcing My New Book!

March 10, 2010 BY danariely

Here is the cover of my new book. Look for it June 1, 2010!

Predictably Irrational — 2 years

February 19, 2010 BY danariely

Predictably Irrational was published two years ago today

Mazal Tov

It has been an amazing two years


Attention Predictably Irrational Fashionistas!

January 15, 2010 BY danariely

One of our readers, Ms. Justine Chiu, has sent me two fantastic pictures of her Predictably Irrational outfit. If anybody else has fun ideas for how to dress Irrationally, please email them to me and I’ll put some more pictures up on my blog.

justinechiu_predictablyirrational_01 08-39-10-1justinechiu_predictablyirrational_02 08-39-10

Help find a name

October 30, 2009 BY danariely

I recently started working on my next book.

It is generally going to be more stories about my research and the plan is to have 3 parts

Part 1: Personal life, happiness, adaptation, dating, and online dating
Part 2: business life: motivation at work, the role of bonuses, mistrust, and revenge
Part 3: cheating: the effects of observing other people cheat, group based cheating, the effect of one dishonest act on others etc.

The current title is:

Living irrationally: the way we work, date and cheat.

If you have any other suggestions for a title, please email me at dan at predictablyirrational dot com

Many thanks


The Nuances of the FREE! Experiment

August 10, 2009 BY danariely

The New York Times and Time Magazine have recently posted interesting articles about two new books that discuss consumer behavior: Chris Anderson’s Free and Ellen Ruppel Shell’s Cheap (see links in The New York Times and Time Magazine).

Both books reference our Hershey’s Kiss experiment that is described in Chapter 3 of Predictably Irrational. If you recall, in one trial of one study we offered students a Lindt Truffle for 26 cents and a Hershey’s Kiss for 1 cent and observed the buying behavior: 40 percent went with the truffle and 40 percent with the Kiss. When we dropped the price of both chocolates by just 1 cent, we observed that suddenly 90 percent of participants opted for the free Kiss, even though the relative price between the two was the same. We concluded that FREE! is indeed a very powerful force.

It’s important to note that we have carried out lots and lots of studies on the effect of FREE!, many of which are detailed in Predictably Irrational. Describing them all, however, would be too much for those who are trying to make just one point abut this effect, so naturally we see authors making choices about which experiments to describe and which ones to leave in footnotes, or not to mention at all. But, some  kinds of omissions are made as well — ones that are important for understanding the complexity of the effect.

For example, in one study of FREE!, we tried lowering the price from 2 cents to one cent on the Kiss to see if we observed that same level of increase in demand in the Kiss. We didn’t. In another study we also tried seeing what would happen if we lowered the price from FREE! to negative one cent, and we also didn’t see a difference in behavior. We also tried the experiment on a broad demographic–not just college students, but also on children and older adults.
Personally, I think it is perfectly fine for people to take the main point from some experiments and build on it, but as readers (and writers) we should realize that often there is more complexity to the picture and that before criticizing particular findings, or citing them as supporting evidence, we should keep in mind the nuances.

Email me the expanded edition of PI!

June 30, 2009 BY danariely

A few people purchased the original version of Predictably Irrational since it came out in February 2008.

Now that the expanded edition is out, it seemed to me that the right thing would be to get the extra material to those who have purchased the book already.  After discussing this idea with HarperCollins, my publisher, we decided to try an honor system for distributing the extra material.

So — if you purchased the original version of Predictably Irrational and you want the extra material, please email  piexpanded@gmail.com and we will email you back the added information in 3 PDFs (a new introduction, added material about the original chapters, and reflections about the financial markets).

Irrationally yours