Decision journaling is a structured practice of documenting significant decisions, assumptions, expected outcomes, and actual results to improve future decision-making quality over time. It originated in behavioral economics and cognitive psychology research, particularly popularized by Farnam Street and the Good Judgment Project, as a method to combat hindsight bias, identify repeated patterns in decision-making, and build calibrated judgment. By creating a written record of what you knew and believed at the time of the decision—before outcomes are known—you preserve the ability to learn objectively from both successes and failures. The core insight: decisions should be judged by the quality of the process and information available at the time, not by results alone, since even excellent decisions can have poor outcomes due to randomness, and vice versa.