Decision journal

A written record of why a decision was made, written at the time it was made, and never edited afterwards.

Example

Four lines before a purchase: what you believe, what you expect, what would tell you that you are wrong, and what you did not have time to examine.

Important

An entry written after the outcome is known is not a decision journal, whatever it is filed as - and it will read better than the contemporaneous one, which is exactly what makes the substitution easy to miss.

Related terms

• Hindsight bias — The tendency, once an outcome is known, to recall having expected it - the genuinely uncertain version of events quietly stops being available.
• Falsifiable claim — A statement specific enough that some future fact could show it to be wrong.
• Investment thesis — A written statement of what you believe about an investment, at what price it is worth owning, and what specific observation would tell you that you were wrong.

Lessons that explain it

• Write the decision down before you know how it turns out — A decision record captures what you decided, why, the conditions, the main risks and what would change your mind. It turns each decision into something you can learn from later. (9 min)
• A memo is a thinking tool before it is a selling document — Two versions of the same memo can describe the same deal and do opposite jobs - one is written to get to yes, the other is written to find out whether yes is correct. (9 min)
• Amend, date and keep the original - never quietly rewrite — A memo is a record of reasoning at a moment. When facts change, add a dated amendment rather than editing the original, so the evolution of your thinking stays visible and reviewable. (10 min)
• Write down why, while you still do not know — Memory does not store your reasoning; it reconstructs it, and it reconstructs it to fit whatever happened. The only honest record is the one made before the outcome existed. (9 min)
• The entry itself: eight lines, five minutes — A template short enough that you will actually use it, and specific enough to be worth reading in three years. Write one by the end of this lesson. (8 min)
• A short review you actually do beats a thorough one you abandon — Decision journals fail through ambition. A fixed, brief monthly pass over recent entries and a longer annual review are enough to produce most of the learning. (9 min)

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