What is reference class forecasting?

Reference class forecasting is a concept in personal epistemology: Add buffer to every estimate and use reference class forecasting.

Example: You estimate a website redesign will take three weeks. You have a clear plan, a motivated team, and no visible obstacles. Eight weeks later, you are still not finished — the design revisions took longer than expected, the CMS migration surfaced data issues nobody anticipated, and two team members were pulled onto an urgent client project. Nothing catastrophic happened. Everything just took longer. When you look back at your last four projects, all of them overran by a factor of two to three. The estimate was not unlucky. It was structurally wrong — built from an inside view of this specific plan rather than an outside view of how projects like this actually behave.

This concept is part of Phase 42 (Time Systems) in the How to Think curriculum, which builds the epistemic infrastructure for time systems.