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Task Times, The Planning Fallacy, and a Magical 20%

Overcoming Bias: Planning Fallacy

Via The Guardian, via Chairman Gruber, comes this post from the new-to-me blog, Overcoming Bias. It discusses the research behind a common cognitive bias known as The Planning Fallacy, which is a repeatable, documented error in thinking that apparently explains why we all tend to "underestimate task-completion times."

It's summed up nicely by Gödel, Escher, Bach author Douglas Hofstadter's Law regarding the time it takes to do anything:

It always takes longer than you expect, even when you take Hofstadter's Law into account.

Sounds familiar. From the Overcoming Bias post:

People tend to generate their predictions by thinking about the particular, unique features of the task at hand, and constructing a scenario for how they intend to complete the task - which is just what we usually think of as planning.


But experiment has shown that the more detailed subjects' visualization, the more optimistic (and less accurate) they become.

Cf: The Optimism Bias.

In my days as a project manager (and in another life as a freelance designer), I got into a habit that has served me well to this day: get the best estimate of both job requirements and time-to-completion that you can find. Then add 20%. Then, when nobody is looking, add another 20%. Then pray.

Although it's no inoculation against the (apparently immutable nature of) Hofstadter's Law -- and you'll still end up short most of the time -- it can help you do one thing much better: manage expectations. Because you're a project manager, not a magician. Magicians get cooler hats.

I think planning a project is ultimately a little like throwing a donut at the moon. You can never actually hit the target, plus you'll be lucky if you aren't hit in the face on the way down.

About Merlin

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Merlin Mann is an independent writer, speaker, and broadcaster. He’s best known for being the guy who created the website you’re reading right now. He lives in San Francisco, does lots of public speaking, and helps make cool things like You Look Nice Today, Back to Work, and Kung Fu Grippe. Also? He’s writing this book, he lives with this face, he suffers from this hair, he answers these questions, and he’s had this life. So far.

Merlin’s favorite thing he’s written in the past few years is an essay entitled, “Cranking.”




An Oblique Strategy:
Honor thy error as a hidden intention


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