Planning Fallacy: Bit Off More Than You Can Chew?

Have You Ever?

Picture this: it’s 6 P.M. on a school night. Your favorite TV show is just about to air a new episode and you really want to know what happens, but you also have an English essay due tomorrow that you haven’t started. With all the commercial breaks included, it’ll be around 7 P.M. when you finish watching the episode. You plan on going to sleep at 10 P.M. You think, No problem - I can totally write an essay in three hours

The next thing you know, it’s 1 A.M. and you’re still at your computer, trying to write a conclusion paragraph. An essay that you thought would take only three hours has actually taken you six hours. Sounds familiar, right?

Here’s Why

Human brains are wired to be overly optimistic when it comes to judging our own efficiency. So the next time you look at a pile of homework and your brain immediately goes, “I can finish that in a couple hours, easy peasy!” you should know that that’s an underestimate of the time it’ll actually take.

Definition of Planning Fallacy

The planning fallacy is a cognitive bias that causes people to underestimate the amount of time they need to complete any given task. 

The Experiment

Psychologists Daniel Kahneman and Amos Tversky were the first to propose the existence of the planning fallacy in 1979. However, it was in 1994 that one of the most famous experiments regarding the planning fallacy was actually conducted by Roger Bueller and Dale Griffin. Bueller and Griffin surveyed a group of college students about how long they thought they would take to write their senior theses. On average, these students estimated that they’d finish in 33.9 days. Bueller and Griffin then asked the students to approximate the absolute minimum and maximum time they could possibly need for their senior theses. The average estimate was 27.4 days for the minimum time and 48.6 days for the maximum time. However, a majority of the students exceeded even the “maximum time limit” that they had given themselves: the actual completion time of the senior theses was 55.5 days, on average.

Although these college students had obviously experienced writing long papers before and witnessed their own procrastination, the knowledge of their previous failures still didn’t stop them from making an over-optimistic prediction for when they’d finish their senior theses. This is one of the most baffling parts of the planning fallacy: people are able to admit their past over-optimism, but they always think that this time it will be different, and they will finally finish the task in the time that they predicted. 

So What?

In 2003, Daniel Kahneman and new research partner Dan Lovallo revisited the idea of a planning fallacy and discovered that people not only underestimate the amount of time they will need to finish certain tasks, but also underestimate the negative consequences and monetary costs of doing a given task. For example, the Sydney Opera House was originally scheduled to be finished in 1963 - however, in reality, the building’s construction took an extra decade and cost nearly a hundred million dollars more than expected. Despite the increased time and money put into the project, the finished Sydney Opera House still ended up being smaller and less grand than originally planned.

Besides large-scale architectural projects, the planning fallacy has repercussions in nearly everyone’s daily life. As we’ve mentioned before, the planning fallacy causes students to underestimate the amount of time that a piece of homework will take to finish, possibly leading them to either pull all-nighters or miss deadlines. Adults are certainly not immune to the planning fallacy either - surveys of taxpayers find that they typically turn in their tax forms a week later than they personally expected. 

Think Further

  1. When was a time you took longer to finish a task than you expected?
  2. Why do you think human brains are wired with the planning fallacy? What do you think might be an evolutionary advantage of having a planning fallacy?
  3. Name a few strategies you might use to make sure you finish assignments on time now that you know about the planning fallacy.


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Learn More

  1. Buehler, Roger, et al. “Inside the Planning Fallacy: The Causes and Consequences of Optimistic Time Predictions.” Heuristics and Biases: The Psychology of Intuitive Judgment, Cambridge University Press, 2002, pp. 250–70. APA PsycNET, doi:10.1017/CBO9780511808098.016.
  2. Kruger, Justin, and Matt Evans. “If You Don’t Want to Be Late, Enumerate: Unpacking Reduces the Planning Fallacy.” Journal of Experimental Social Psychology, vol. 40, no. 5, Sept. 2004, pp. 586–98. ScienceDirect, doi:10.1016/j.jesp.2003.11.001.
  3. Procrastination and the Planning Fallacy: An Examination of the Study Habits of University Students – ProQuest.