"Why Did We Choose That?" How to Keep a Tiny Record of Your Decisions and Their Reasons

A personal decision log is a short note you write when you make a choice. It has three lines: what you chose, what else you considered, and why. It takes under a minute, and it means that a year from now, when someone asks "why did we pick this?", you have the real answer instead of a guess.

The rest of this guide covers why your memory is unreliable here, what to put on each line, real examples from ordinary life, and how to read the log back without kicking yourself.

Why "why did I decide that?" is so hard to answer later

Many decisions come back around. The insurance renews. The phone contract ends. The second child reaches school age. You sit down to choose again and realize you don't remember how you chose last time.

Part of that is plain forgetting. You might have compared four plans over two evenings, but the details were never meant to last. You kept the decision and dropped the reasons.

There's also a quieter problem, and it's worth explaining carefully.

Hindsight bias, in plain terms

Psychologists use the term hindsight bias for the "I knew it all along" feeling. Once you know how something turned out, it starts to seem obvious. It can also bend your memory of what you thought before.

The classic evidence comes from Baruch Fischhoff's work in the 1970s. In one study, people estimated how likely various outcomes of President Nixon's 1972 trips to China and the USSR were before the trips happened. Afterwards they were asked to recall their own estimates. As Scientific American describes it, people gave retroactively higher probabilities to events they believed had happened and lower ones to events they believed hadn't. They stayed convinced they were reporting their earlier judgments accurately.

A 2012 review by Neal Roese and Kathleen Vohs describes hindsight bias as working on three levels. As summarized by ScienceDaily, these are misremembering an earlier opinion, believing the outcome was inevitable, and believing you personally could have foreseen it. The authors argue that the bias "gets in the way of learning from our experiences."

A fair caveat: these are mostly lab and survey studies, about predictions and events. Nobody has measured exactly how much your memory of choosing a broadband plan will drift. But the pattern plausibly applies to everyday choices too. If the plan turns out badly, it's easy to feel you "should have known." If it goes fine, it's easy to forget the hard trade-off you made.

A note written at the time is much less likely to drift. That's the main reason to write down why you made a decision.

The three-line personal decision log

Here's the format. Each entry is three lines, plus a date.

1. Chose: what you picked.
2. Also looked at: the other options you seriously considered.
3. Because: the one to three reasons that actually tipped it.

Professional decision journals, like the Farnam Street template, ask for much more: the context, the expected outcomes, and how confident you are. That can be useful for an investor. For choosing a dentist, it's a form few people would fill in twice.

Three lines is small enough that you'll actually do it.

Line 1: what you chose

Be specific enough that future you can find the exact thing. "Fibre 500 plan, 24-month contract" beats "the internet." Include a name, a model or a plan tier if there is one.

Line 2: what else you considered

This is the line people skip, and it's the most useful one. Without it, your log only says what you did. With it, you can see what you turned down.

It also fits the advice in the Roese and Vohs review. They suggest "considering the opposite", meaning thinking through how other outcomes could have happened, as one way to counter hindsight bias. Writing down the options you rejected keeps them visible later, so the choice you made doesn't look like the only one that was ever possible.

Keep it short. Name each option and, if you can, the one reason it lost.

Line 3: why

Write the real reason, not the tidy one. "The other school's pickup time would have meant leaving work early every day" is more honest, and more useful, than "better fit."

One to three reasons is usually right. If you have ten, the decision probably came down to two of them. Write those.

Real examples from ordinary life

Here's what a week of entries might look like. The prices and names are made up, but the shape is the point.

Notice what each "because" does. It records a fact you'd otherwise lose: the neighbour's dropped calls, the waitlist, the courtesy car. Those are exactly the details that tend to vanish in a year.

The job-offer entry shows something else. Sometimes the decision is to say no, or to keep things as they are. Those are worth logging too. "Why didn't I take that job?" is an easy question to keep asking yourself.

If a decision came from comparing quotes or viewings, your notes from that process are the raw material. Guides on what to write down on each contractor visit or keeping apartment viewings from blurring together cover that earlier stage. The decision log is the one-paragraph summary at the end.

Which decisions are worth a log entry

You don't need to log what to have for dinner. A good rule: log a decision if you'll face it again, or if someone might ask you about it later.

Good candidates:

• Renewals: insurance, phone contracts, internet, energy plans, subscriptions.
• Family choices: schools, childcare, clubs, which doctor or dentist.
• Bigger purchases: cars, appliances, laptops, a mattress.
• Money moves: which savings account, whether to overpay a mortgage.
• Work: job offers, saying yes or no to a project, a process you changed.
• Health and care: choosing between treatment options or care providers, with the reasons the professional gave you.
• Shared decisions: anything you decided with a partner, housemate or sibling, where you might later remember it differently.

That last one matters more than it sounds. Two people can remember the same conversation in two ways. A dated note of "we picked this because" settles things gently.

When to write it, and where to keep it

The best moment is right after you decide, before the outcome is known. Once you know how it turned out, hindsight can start to color your memory. Write it when you click "buy," sign the form or send the email.

If that's not possible, do it the same day. Saying it out loud works fine too. A 20-second voice note ("chose the fibre plan, looked at cable and 5G, cable dropped calls next door") holds the same three lines.

Where you keep it matters less than whether you can find it later. Some options:

• A single running note in your phone's notes app, newest entry at the top.
• A paper notebook kept with your household paperwork.
• An email or text to yourself with a consistent subject like "Decision:".
• A spreadsheet if you like columns, using the table above as a template.
• A capture app with plain-language search, such as EyeNotes, if you'd rather ask for an entry than scroll to it.

Whatever you use, put a word like "Decision" or "Chose" at the start of each entry. Then a search for that word pulls up the whole log. If you've ever lost a note you knew you wrote, this guide to finding a note when you only remember part of it helps.

It's also worth keeping the decision near the paperwork. If you log a laptop purchase, the receipt and warranty details are worth storing alongside it.

Reading it back without beating yourself up

A personal decision journal is only useful if you look at it again. The easiest trigger is the decision coming round again. Insurance renewal arrives, you search "Decision: car insurance," and there are last year's reasons.

When you read an old entry, ask three questions:

1. Are the reasons still true? Maybe the courtesy car mattered when you had one vehicle, and now you have two.
2. Did the thing I worried about happen? Did the 5G signal really matter, or did you move the router?
3. Was the choice reasonable with what I knew then?

That third question is the kind one, and it's where hindsight bias likes to sneak in. A choice can be sensible and still turn out badly. The school you picked might lose its after-school club next year. That doesn't make your reasoning wrong. Your note shows what you knew at the time, which is the fair way to judge it.

The reverse is true too. If something worked out, check whether it worked out for the reasons you wrote down. Sometimes you got lucky. That's worth knowing before you choose again.

Optional extras, if three lines feel too thin

Once the habit sticks, some people add one more line. Pick whichever helps you most:

• Expecting: what you think will happen. "Bill should stay under 40 a month."
• Check again: a date or event. "Contract ends March 2028."
• Confidence: a rough gut number. "70% sure this is right."
• Who said what: useful for advice from a doctor, a teacher or a mechanic.

Each one makes the entry more useful at review time. But don't let the extras become a reason to skip the entry. A three-line note you actually write beats a ten-field template you abandon after a week.

The short version

Next time you make a choice you'll face again, take one minute and write it down:

• Chose: what you picked.
• Also looked at: what you turned down.
• Because: the real reasons.

Date it, keep it somewhere you can search, and look at it when the decision comes back. You'll stop asking "why did I decide that?" and start building on what you already worked out.