Decision quality = Evidence × Repeatability × ReviewWhen you buy and when you sell can matter more than what you pick. A research routine exists to keep you invested through the dips.
Decision History
The honest, time-stamped record of what you decided and why — the only reliable way to learn from your own investing.
What is a decision history in investing?
A decision history (or decision journal) is a time-stamped log of every investment decision — buy, sell, trim, add, or pass — recorded with the thesis, the price, and your emotional state, written before the outcome is known. It exists because memory is unreliable: a contemporaneous record fixes your reasoning so it can be judged honestly later.
- Each entry captures the action, price, thesis, key risk, and how you felt.
- It separates good decisions from lucky ones, and bad decisions from unlucky ones.
- It records why you acted — not just returns — which is what actually improves a process.
Definition
A decision history (or decision journal) is a running log in which you record each investment decision — buy, sell, trim, add, or pass — together with the thesis, the price, and your emotional state at the time. Crucially, it is written before the outcome is known.
It exists because memory is unreliable and self-serving: after the fact we rewrite why we acted. A contemporaneous record fixes the reasoning in place so it can be judged honestly later.
How to keep one
For each decision, capture five things: what you did, the price/level, the core thesis in a sentence or two, the key risk that would prove you wrong, and how you felt (calm, fearful, FOMO). Months later, return and grade the result against the original reasoning — separating good decisions from merely lucky ones, and bad decisions from merely unlucky ones.
Simple example
On review you notice every "anxious, bought because it was running" entry underperformed, while "calm, bought below my estimate of value" entries did well. That pattern — invisible without a record — tells you the single most valuable thing about your own process: when to trust yourself, and when to wait.
Common misconception
"A decision history is just tracking my returns." Returns tell you what happened; a decision history tells you why, and whether your reasoning was sound regardless of outcome. A profitable decision made for the wrong reasons is a future loss waiting to repeat — only the reasoning, not the P&L, reveals that.
- 1Each entry captures the action, price, thesis, key risk, and how you felt.
- 2It separates good decisions from lucky ones, and bad decisions from unlucky ones.
- 3It records why you acted — not just returns — which is what actually improves a process.
| Shortcut | The honest, time-stamped record of what you decided and why — the only reliable way to learn from your own investing. |
|---|---|
| Disciplined workflow | Each entry captures the action, price, thesis, key risk, and how you felt. → It separates good decisions from lucky ones, and bad decisions from unlucky ones. → It records why you acted — not just returns — which is what actually improves a process. |
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True story · The Magellan paradox
A 29%-a-year fund whose average investor did far worse
From 1977 to 1990 Peter Lynch ran Fidelity Magellan to roughly 29% a year — the best long-run record of any large mutual fund; $10,000 left alone became about $280,000. The fund's door was open to everyone, and millions walked through it.
Yet Fidelity's own analysis found the average dollar invested in Magellan earned dramatically less — many investors actually lost money. Cash flooded in after hot streaks and fled after every dip, so most owners systematically bought high and sold low. The fund's return and its investors' returns were two different numbers.
When you buy and when you sell can matter more than what you pick. A research routine exists to keep you invested through the dips.
≈29%/yr1977–1990
≈28×in thirteen years
worsethe average holder's result
True story · Michael Burry, 2005
A thesis is only real once it is written down
In 2005 Michael Burry concluded that subprime mortgage bonds would default at scale — and he did not just trade the idea, he documented it. His investor letters laid out, in writing, exactly what the bet was, why the market was mispricing it, what would kill the thesis, and what evidence would confirm it: loan-level default data, teaser-rate reset schedules, the works.
Then everything went against him. The bonds did not fall for two years; investors revolted and demanded their money back. What held the position together was the memo: the reasons on paper had not changed, so the position did not change. When the collapse came in 2007–08, his fund returned nearly 500% cumulatively. The investors screaming loudest had been refuted not by Burry's feelings but by his own written record.
A written memo is the only defense against your future self. If the written reasons still stand, hold; if they break, sell — feelings get no vote.
2005thesis written in advance
2 yrsof being early and doubted
≈489%cumulative fund return
True story · Buffett, 1969
The courage to do nothing
At the top of the speculative "Go-Go" years, Buffett — after thirteen years compounding near 30% with no down year — wrote to his partners that he no longer understood the market and could find nothing sensible to buy. Rather than lower his standards, he closed the partnership and handed back the money at the peak of his fame.
Then he waited. When the 1973–74 crash finally arrived, he was liquid while everyone else was forced to sell, and described feeling "like an oversexed man in a harem" — buying the Washington Post and other franchises at panic prices that set up the next thirty years.
Cash and patience are positions too. Standards only count if you keep them when it is hardest.
≈30%/yrfor thirteen years
1969returned the money
1973–74redeployed into the crash
Related tools
Frequently asked questions
How is a decision history different from a portfolio tracker?
A portfolio tracker records positions and returns; a decision history records the reasoning and emotional context behind each decision, written before the outcome. One measures results, the other improves the process that produces them.
When should I review my decision history?
Review individual entries when an outcome becomes clear, and review the whole log periodically (e.g. quarterly) to spot recurring patterns in when your judgment is reliable versus when emotion drove the call.
Keep a decision history that turns hindsight into skill:
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