ThinkCritical.eu · Manipulation atlas
Group decisionsPlanning fallacy
An optimistic “this time will be different” ignores how similar projects turned out.
When we plan, we picture everything going smoothly and overlook how long similar efforts took and what they cost in the past. That's why renovations, building projects and school projects so often run late and over budget. The term was coined by the psychologists Daniel Kahneman and Amos Tversky.
A town plans to renovate its community hall: “Done in six months, budget €300,000.” The last three similar renovations in the area took 14 to 20 months and cost a third more. Asked why this one would be faster, the answer is just: “This time we've got a good contractor.”
How to spot it
- “This time will be different”, with no concrete reason for what has changed.
- The plan only allows for the best-case scenario, with no time or money in reserve.
- Nobody checked how similar projects went elsewhere or in the past.
- Past delays are put down to “bad luck” rather than treated as lessons.
How to check and what to do
- Find 3–5 similar projects and check how long they actually took and what they cost. That's your starting estimate (the outside view).
- Only then adjust the estimate for the ways your project demonstrably differs.
- Add a reserve of time and money, and write down what it's based on.
- Ask: “What happened last time – and what exactly will we do differently?”
Tip: It works at home too: how long did your friends' bathroom renovation really take?
Full explanation and exercises:
thinkcritical.eu/en/manipulation-atlas/planning-fallacy