Planning fallacy
🧩EXPLANATION
The tendency to underestimate how long a piece of work will take, even when you know that similar work has overrun before. Kahneman and Tversky named it in 1979. The cause, as 📕 Thinking, Fast and Slow tells it, is the inside view: you build the estimate from the plan in front of you, step by step, and each step looks reasonable.
What the inside view leaves out is everything not yet imagined: the illness, the dependency, the load test.
His own story is a textbook his team expected to finish in about two years. It took eight.
Example from work: 18 February. The plan was sound and I could defend every line of it. We launched on 11 March.
Often confused with: optimism or sandbagging. It survives in careful pessimists, because it is about where the estimate comes from, not mood. The cure is 🧩 The outside view.
- Notes: 📖 Kahneman on the planning fallacy, written twelve days after the launch
- The numbers behind it: 📰 Why software projects take longer than you think
- Company for the bad weeks: 🎙️ Cautionary Tales
- My claim: 💎 My launch estimates ignore every launch I have seen