guide
how to keep a decision journal
A decision journal is a record of your decisions made at the moment you make them: what you chose, why, what you expected, and how confident you were. Not a diary of what happened, but a snapshot of your thinking before you knew the outcome. Daniel Kahneman, who won the Nobel Prize for his work on judgment, called it the single best way to improve decision-making, because it is the only defense against hindsight bias.
Why bother
Memory is not an archive; it is a press office. Once you know how things turned out, your recollection of what you believed quietly shifts toward “I saw it coming” or “nobody could have known.” Psychologists have replicated this for fifty years. The result: you never learn whether your judgment is actually good, because the evidence gets edited before you review it. A journal freezes the evidence.
The template
Five fields, two minutes. Log it before the outcome is known:
One sentence. What did you choose to do?
Why this option? What were the two or three factors that actually drove the call?
The observable outcome that would make you say this worked.
A number between 50% and 99%. This is the part memory will try to rewrite, so write it down.
When will you know? A week for small calls, a quarter or a year for big ones.
What to log
Anything with a real fork in the road and an outcome you will eventually observe: hiring, job changes, pricing, launches, big purchases, vendor picks, investments of time or money. Add quick predictions too, small calls that resolve in days. They feel trivial, but they build your calibration data twenty times faster than decisions that take a year to play out.
The review is the product
On the review date, answer three questions. Did it go as expected? What actually happened versus what you wrote? What is the one lesson? Grade honestly, including the partial credit cases. Over twenty or thirty reviews a pattern emerges: the domains where your gut is reliable, and the ones where your 90% is really a 60%. That pattern, plotted, is your calibration curve, and your Brier score compresses it into one number you can actually improve.
Why paper journals fail
The failure mode is never the logging; it is the follow-through. Nobody flips back to page 40 nine months later. The fix is a reminder that arrives on the review date without you remembering anything. That is the part Brier automates: log the decision in two minutes, and an email finds you when it is time to grade it. The confidence number is locked once logged, so hindsight cannot touch it.