A decision log can make an investment thesis easier to review over time. It does not need to be a detailed model. A short, dated note is often enough to show what was known, what was assumed, and what would prompt another look.
I use four sections:
The question
State the decision or idea in plain language. Avoid mixing the question with the conclusion.Evidence and assumptions
Separate observable information from conditions you expect to hold. For example, a reported operating result is evidence; an expectation about future demand is an assumption.Uncertainties to monitor
List the factors that could materially affect the reasoning. Keep this focused. The purpose is to make uncertainty visible, not to create an endless checklist.Review conditions
Write down what new information would lead you to revisit the thesis. This helps prevent an old conclusion from becoming fixed simply because it was written down before.
A log like this will not make a decision correct, and it cannot remove risk. Its value is more modest: it provides a clear record of the reasoning available at the time and makes later review more deliberate.
The format can be as simple as a note with a date, a few bullets, and a review date. What matters is using the same distinctions consistently: evidence, assumptions, uncertainty, and conditions for review.
