The Planning Fallacy
Why You'll Finish This Lesson Faster Than You'll Finish That Project
The Sydney Opera House was budgeted for four years and finished in fourteen — and that's not an exception, it's practically the rule.
The Idea
In 1979, Daniel Kahneman and Amos Tversky named something we'd all been doing forever: systematically underestimating how long our own projects will take, how much they'll cost, and how many obstacles will appear — while simultaneously overestimating how smoothly everything will go. They called it the planning fallacy, and what makes it genuinely strange is that it isn't simply ignorance. People who have been late on every project they've ever run will still produce optimistic timelines for the next one. The error persists even when you know about it. The reason it's so stubborn lies in how we imagine the future. When we plan, we picture a sequence of steps going right — we're essentially telling ourselves a story with a satisfying ending. What we don't do is simulate the full distribution of possible futures: the illness, the software problem, the dependency that stalls everything. We plan for the best-case scenario while believing we're planning for the realistic one. Kahneman later proposed a partial antidote he called the 'outside view': instead of reasoning from the inside of your specific plan, ask how long projects like this actually take for other people. Strip away the details that make yours feel special, find the base rate, and anchor to that. It sounds almost insultingly simple — but it works, precisely because it bypasses the storytelling trap and forces a confrontation with reality.
In the World
In the early 1990s, Kahneman himself was part of a team designing a new curriculum for Israeli high schools. Partway through the project, he asked each team member to write down their private estimate for when they'd be finished. Answers clustered around two years. Then he turned to the one member with the most experience in curriculum development and asked a different question: of similar projects you've seen, how many actually finished on time, and how long did they typically take? The expert paused, then admitted that he couldn't recall a single comparable project finishing on schedule. Most took seven to ten years. A few were abandoned entirely. The room went quiet. The team continued anyway — and finished in eight years. What's remarkable about this story isn't the outcome, it's the moment of recognition. Here was a group of intelligent, experienced professionals who already knew the relevant data and still couldn't override their optimism once they were inside the plan. The outside view had to be deliberately summoned; it didn't arise naturally. This is the planning fallacy at its sharpest: not a failure of information, but a failure of perspective. The inside view feels more real, more personal, more responsive to the genuine ambition of what you're trying to build. The outside view feels cold and beside the point. But cold is often exactly what you need.
Why It Matters
Understanding the planning fallacy won't make you a pessimist — it's an invitation to become a more honest and effective one. The goal isn't to dread every undertaking but to build in what engineers call slack: the quiet buffer that turns a setback into a manageable delay rather than a crisis. On a personal level, it's worth sitting with the question of why the inside view feels so compelling. Part of the answer is motivational — optimistic timelines get projects started, and starting matters. But part of the answer is ego: admitting that your project is just another project, subject to the same friction as everyone else's, requires a small act of humility that's harder than it looks. The practice, then, is twofold. Before committing to a timeline, actively seek the base rate — ask someone who's done something similar, look at your own history with honesty. And when you're deep inside a project and everything feels on track, consider whether that feeling is signal or story. Often it's both, but knowing the difference is most of the work.
A Question to Ponder
When you picture a project going well, are you imagining what you hope will happen or what the evidence suggests is likely — and do you actually know the difference?
Get a new one of these every morning.
Start learning with Thinkable