A Day Late and a Dollar Short: The Planning Fallacy Explained

Why do we systematically underestimate the amount of time or money we are going to spend on a given project? 

One of the most universal and robustly demonstrated cognitive biases is the planning fallacy.  If you’ve ever underestimated how long it would take you to finish writing that paper you’re working on or finish moving or get to your destination, then congratulations, first of all you’re a human being and that makes you subject to the planning fallacy.


So why does this happen?  Why do we systematically underestimate the amount of time or money we are going to spend on a given project?  

One piece of the puzzle is the fact that our intuitions aren’t very good at thinking about compound probabilities.  So here’s what that means.  If you think back to the last time you were late completing some errand that you were running and you also think back to how you formed your prediction of how long the errant would take – if you’re like most people, you probably thought briefly about the various steps that make up the task of running an errand like getting ready to go, driving to the store, finding the thing I’m looking for, waiting in line, getting in my car and coming back home.

If you’re like most people you probably envisioned a typical occurrence of each of those steps - so a typical amount of time it takes you to get ready to go or a typical amount of time it takes you to find parking.  That’s what formed your rough estimate of the amount of time the whole errand would take.  And in most cases you’re going to be correct about your typical estimate.  That’s what makes it typical.

But the more steps you have in whatever project or task you’re working on, the greater the chance that in one of those steps you’re going to hit a snag and it’s going to turn out to be atypical. 

That probability that the whole thing is going to be atypical in some respect goes up the more steps you have in the process.  And it goes up faster than our intuition would predict.  One way to tell that this process is partly responsible for the planning fallacy is that when scientists ask people how long would you expect this project to take you if it progressed in a typical fashion, people give estimates that are almost identical to the estimates that they give when scientists ask how long would you expect this project to take if nothing goes wrong. 

In Their Own Words is recorded in Big Think's studio.

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Scientists study tattooed corpses, find pigment in lymph nodes

It turns out, that tattoo ink can travel throughout your body and settle in lymph nodes.

17th August 1973: An American tattoo artist working on a client's shoulder. (Photo by F. Roy Kemp/BIPs/Getty Images)
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In the slightly macabre experiment to find out where tattoo ink travels to in the body, French and German researchers recently used synchrotron X-ray fluorescence in four "inked" human cadavers — as well as one without. The results of their 2017 study? Some of the tattoo ink apparently settled in lymph nodes.


Image from the study.

As the authors explain in the study — they hail from Ludwig Maximilian University of Munich, the European Synchrotron Radiation Facility, and the German Federal Institute for Risk Assessment — it would have been unethical to test this on live animals since those creatures would not be able to give permission to be tattooed.

Because of the prevalence of tattoos these days, the researchers wanted to find out if the ink could be harmful in some way.

"The increasing prevalence of tattoos provoked safety concerns with respect to particle distribution and effects inside the human body," they write.

It works like this: Since lymph nodes filter lymph, which is the fluid that carries white blood cells throughout the body in an effort to fight infections that are encountered, that is where some of the ink particles collect.

Image by authors of the study.

Titanium dioxide appears to be the thing that travels. It's a white tattoo ink pigment that's mixed with other colors all the time to control shades.

The study's authors will keep working on this in the meantime.

“In future experiments we will also look into the pigment and heavy metal burden of other, more distant internal organs and tissues in order to track any possible bio-distribution of tattoo ink ingredients throughout the body. The outcome of these investigations not only will be helpful in the assessment of the health risks associated with tattooing but also in the judgment of other exposures such as, e.g., the entrance of TiO2 nanoparticles present in cosmetics at the site of damaged skin."

Photo by Alina Grubnyak on Unsplash
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