Tuesday, March 05, 2019

We’re terrible at predicting time, so do these things instead

I noticed when I was programming that it usually took me about 3 times as long to finish writing and testing a program as I thought it would, so I started multiplying by 3 when giving an estimate. My customers liked me because I met my estimates. But many/most people never did learn.


By Jessica Greene—Zapier
Feb. 28, 2019


The planning fallacy is a term used by psychologists to describe our tendency to underestimate the amount of time it will take to complete a task. The term was first coined in 1977 by psychologists Daniel Kahneman and Amos Tversky.

Kahneman and Tversky explained that people have a tendency to disregard historical data when making predictions. Instead of forming estimates based on historical evidence (it always takes a month to paint a room), we focus solely on the upcoming task (this room is small, so it won’t take long to paint).

Kahneman later expanded on the original idea in his 2011 book Thinking Fast and Slow. In it, he argues that estimation mistakes can usually be attributed to two key factors:

Failing to consider how long it’s taken us to complete similar tasks in the past
Assuming that we won’t run into any complications that will cause delays

But it’s not all bad news. If you understand the reasons why we tend to underestimate how long tasks will take, you can take steps to avoid the pitfalls of the planning fallacy and start forming more realistic estimates.


The following six estimation techniques are all designed to help you avoid underestimating when you’re trying to determine how much time a task will take.


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