The Planning Fallacy

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The Planning Fallacy is a cognitive bias that causes people to underestimate the time and resources needed to complete a task. Despite past experience showing that similar tasks have typically taken longer than planned, individuals often predict that their own projects will proceed more smoothly. This fallacy is common in both personal and professional settings and can lead to missed deadlines, budget overruns, and increased stress.


Imagine you’re writing a blog post on a topic you’re familiar with. You estimate that it will take you two hours to complete the post, including research, writing, and editing. Based on the Planning Fallacy, you’re likely underestimating the time required. In reality, the process might involve unforeseen complications like:

  • Additional time for in-depth research
  • Multiple rounds of editing and proofreading
  • Technical issues, such as website downtime or formatting problems
  • Interruptions or distractions

As a result, the blog post might actually take four or five hours to complete, rather than the initially estimated two hours.

Real-World Examples

1. Construction Projects

One of the most cited examples is the construction of the Sydney Opera House. Initially estimated to be completed in 1963 at a cost of $7 million AUD, it was finally completed in 1973 at a cost of around $102 million AUD.

2. Software Development

Many software projects suffer from the Planning Fallacy. For instance, Microsoft’s Windows Vista was initially planned for release within two years but ended up taking over five years to develop.

3. Public Transportation

The “Big Dig” in Boston, USA, was initially estimated to cost $2.8 billion and take a decade to complete. It ended up costing over $15 billion and took 15 years to finish.

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