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 read · Level 4
The journal is not the useful part; rereading it is. I think that is why so many well-designed journals produce nothing - the design effort goes into capture, when almost all the value is in a short, boring, repeated act of going back. Twenty minutes a month, done for years, will teach you more about your own judgement than any book.
Most decision journals are abandoned within a year, usually because the review process was too heavy to sustain.
A schedule that survives:
Frequency Task Time Monthly read entries from 12 months ago, mark outcomes 20 minutes Annually look for patterns across the year 1 to 2 hours
The monthly pass answers three questions per entry:
1 What has happened since? 2 Was the reasoning sound, separately from the outcome? 3 Which stated assumption turned out wrong?
The annual review looks across entries rather than at them individually:
Pattern to look for Example finding Repeated reasoning errors consistently overestimating how fast companies grow Situations where you do well patient decisions in familiar industries Situations where you do badly decisions made under time pressure Calibration how often things you called likely actually happened
Calibration is worth measuring simply. If you tagged ten decisions as likely to work and four did, your confidence is running ahead of your results - a specific, fixable finding.
Because the value of a journal comes entirely from rereading it, and rereading is the part that gets dropped. A twenty-minute monthly habit produces more learning than an elaborate system used twice.
Reviewing entries about a year old also works better than reviewing recent ones: enough has happened to judge, and hindsight has not yet rewritten your memory of what you thought.
Educational, not personalised financial advice. Nothing in the Investor Academy is a recommendation to buy, sell or hold anything — what is right for you depends on your own circumstances and the rules where you live.
An annual review across 22 entries.
Finding Evidence Overestimated growth in 7 of 9 investment decisions projected rates exceeded actual in each Best outcomes in familiar sector 5 of 6 decisions there went as expected Worst outcomes under deadline pressure 4 decisions made within a week, 3 disappointing Calibration: 10 tagged likely, 6 worked confidence slightly ahead of results
The investor made two changes: applying a discount to their own growth assumptions, and refusing to decide within a week unless the opportunity genuinely could not wait. Both came from the pattern across entries, not from any single decision.
Designing an elaborate journal format, using it for three months and never rereading it. The format matters far less than the habit of returning to entries.
Twenty minutes, reading entries from about twelve months earlier.
Record what happened and, independently, whether the reasoning was sound.
Note how likely you thought success was, so calibration can be measured later.
Review across entries for repeated errors, strong areas and conditions that produce poor decisions.
Pick a single adjustment for the coming year rather than a long list.
Once you have kept a decision journal for a year or more and want to extract learning from it.
Do not review entries so recent that outcomes are unclear. Judging a decision after a month usually measures luck.
Research on forecasting accuracy, including work associated with large forecasting tournaments, has found that people who record predictions, track outcomes and review their errors systematically tend to improve their accuracy over time, while those who rely on memory of past judgements generally do not.
Improvement comes from structured feedback on recorded predictions, not from experience alone.
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