Vincent Harrowell: A Simple Decision Log for Tracking Investment Assumptions

Vincent Harrowell — Wed, 21 Oct 2026 04:30:10 +0000

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.

Vincent Harrowell: A Simple Way to Examine an Idea

Vincent Harrowell — Fri, 16 Oct 2026 09:40:27 +0000

A useful idea should be clear enough to examine. When I’m working through a question, I try to make the reasoning visible before I settle on a conclusion.

I use three prompts:

What evidence supports the idea? Start with the information available. Separate what has been observed from what is inferred. If there are gaps, name them instead of quietly filling them with assumptions.
Which assumptions matter most? Most conclusions depend on expectations. Writing those expectations down helps show how much they influence the overall view. It also makes it easier to revisit the reasoning if circumstances change.
What could lead me to reconsider? This question keeps a conclusion open to new information. The answer might be contrary evidence, a different explanation, or a change in the situation. If no possible information could change the view, it may be time to check whether the idea has been examined fairly. These prompts are simple, but they make it easier to explain how I reached a conclusion and what remains uncertain. They don’t remove uncertainty or guarantee that a decision will be right. They help keep the process thoughtful and open to review.

DEV Community: Vincent Harrowell

Vincent Harrowell: A Simple Decision Log for Tracking Investment Assumptions

Vincent Harrowell: A Simple Way to Examine an Idea