This will probably take you longer to read than you think…

Chances are, you are like most other students and have been stuck in the library with one hour to go till your deadline, furiously typing away because you started your report just a tad too late. Maybe that is the case right now. I’m sure you were thinking about the report long before it was due, but you just didn’t expect it to take you as long as it did.

Fortunately it was just a bit of coursework and although you spent all night in the library and maybe five or ten quid on some energy drinks and skittles, it’s just one night. It could be worse, you could have spent $102 million on something that you planned to have only cost $7 million. That was the case with the Sydney Opera House, which also took an extra 6 years to build, and even then, it was a scaled down version compared to what was originally planned.

Another classic example of how bad we are at planning is the Olympic stadium in Montreal. It was planned to be completed for the 1976 Olympics, costing $120 million, and featuring the world’s first retractable roof. Although the stadium was completed in time for the Olympics, the roof wasn’t. It was eventually completed in 1989, 13 years later, and costing $120 million itself! The whole stadium cost $1.1 billion!

These examples perfectly sum up the planning fallacy, that is, our inability to realise, and plan for, how long something will take, or how much it will cost (Kahneman & Tversky, 1979a). Studies looking at this usually entail asking people to estimate how long something will take. One estimate must be as accurate as possible, one as if everything went to plan, and one if everything went horribly wrong. Buehler, Griffin, and Ross (1994, Study 1) did exactly this with a group of final year psychology students who were in the process of writing their dissertations. They found that, on average, students finished 22 days later than their best prediction, 28 days later than their ‘accurate’ prediction, and, most interestingly, 7 days later than their worst prediction. The planning fallacy also occurs with more mundane tasks too, such as doing household chores (Buehler et al., 1994).

The reason we are so bad at planning is because we take what is known as the ‘inside view’ (Kahneman, 2011). This is where we focus on the specifics of the task at hand and draw a start-to-end plan. This fails us because we do not consider all the possible ways in which the future can unfold and instead focus on the best case scenario. What we should do is take the ‘outside view’, where we look at previous tasks of a similar nature and use their statistics to create a baseline for our prediction. Then we can use the specifics of our task to nudge this baseline ever so slightly one way or another.

So when you are doing your next report, or essay, or more importantly, your dissertation, ask others how long theirs have taken them. Even if you think you are smarter than them, it is likely that whatever they say will be much closer to how long it actually takes you than your own estimate.

Toby Johnson



  • Buehler, R., Griffin, D., & Ross, M. (1994). Exploring the “Planning Fallacy”: Why People Underestimate Their Task Completion Times. Journal of Personality and Social Psychology, 67(3), 366-381.
  • Kahneman, D. (2011). Thinking, Fast and Slow. UK: Penguin Books.
  • Kahneman, D., & Tversky, A. (1979a). Intuitive Prediciton: Biases and Corrective Procedures. TIMS Studies in Management Science, 12, 313-327.

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