Ask 'how long have similar tasks taken?' not 'how long…
When planning task duration, deliberately switch from inside-view scenario construction to outside-view base-rate consultation by asking 'how long have similar tasks taken?' instead of 'how long will this take?'
When This Fires
- Estimating duration for any task, project, or deliverable
- During sprint planning, project estimation, or deadline setting
- When your estimate feels confident and detailed (high inside-view activation)
- Complements Decompose tasks into steps before estimating — holistic… (decompose before estimating) and Apply your documented error factor to timeline estimates… (correction factor)
Common Failure Mode
Using the inside view and then "adjusting" with outside-view data: "My scenario says 3 days, but similar tasks took 6, so I'll say 4.5." This anchors on the inside-view estimate and insufficiently adjusts. The outside view should be the anchor: start with "similar tasks take 6 days" and only adjust downward if you can identify specific, concrete reasons this task is different.
The Protocol
When estimating task duration: (1) Ask: "How long have similar tasks taken?" Identify 3-5 comparable past tasks and note their actual durations. (2) Calculate the average. This is your outside-view baseline. (3) Ask: "Is there a specific, concrete reason this task will take less time than the reference class?" Not "I feel good about this one" — a specific, articulable reason (smaller scope, familiar technology, no dependencies). (4) If you can articulate a specific reason → adjust the baseline modestly downward. If not → use the baseline. The outside view is almost always more accurate than the inside view.