The man who wrote everything down

Ask most people how their week went and they will tell you how it felt. Ask them how much they earned, how many hours they worked, or which day was the best, and many will guess. They will say "about 400" or "more or less the same as last month."

This is the story of a man who guessed for nine years, and what happened when he stopped.

Where the guessing started to hurt

The trouble came in small ways. A few times a year he ran short on rent money and could not work out why. He was busy. He was tired. He felt like he was working hard. So where was the money?

His wife asked a simple question one evening: "If it's 600 a month, why do we never see 600?" He did not have an answer. He had never written the number down. Not once in nine years.

He did not want to set up a spreadsheet. He came home at eight or nine at night. He was not going to sit at a computer. So he made a deal with himself that felt small enough to keep.

Three lines a day

He bought a cheap notebook and kept it next to his bed. Every evening, before he slept, he wrote three lines. No more.

• What I did: where he worked, what time he started, what time he stopped.
• What came in: the money, after he paid for stock, fuel and the stall fee that day.
• How I felt: one word or a short phrase. "Tired." "Good." "Wasted day."

Some nights he wrote in two minutes. Some nights he forgot and wrote two days the next morning. He did not make it perfect. He just kept going.

What six weeks of notes showed him

Three patterns came out. None of them matched what he remembered.

There was a fourth pattern he did not expect. On days after he stayed up late on his phone, the "how I felt" line said "tired" or "slow," and the money line was lower. It was not every time. But it was often enough that he could not ignore it.

The biggest shock was the 190 gap between 600 and 410. Over a year that is about 2,280 he thought he had but never did. That was the missing rent money.

Why memory got it wrong

Karim was not lying to himself. His memory was doing what memory does. Psychologists have studied this for a long time. Research suggests that we remember the most intense moments and the endings of events far better than the plain, ordinary parts. A crowded, stressful Saturday leaves a strong mark. A calm Tuesday of packing boxes leaves almost none.

So when he thought "what are my best days," his mind showed him the loud ones. Loud is not the same as profitable.

Memory also rounds numbers in a friendly direction. "About 600" felt true because he had some months close to 600. He forgot the slow months, the returned items, the fuel he paid on his own card.

A written record does not pick favourites. It just sits there. That is why it is useful.

What he changed

He did not quit the market. He made a few small changes and kept writing.

1. He started the online packing first thing on his free mornings, before 9, because the notebook said those were his best hours.
2. He dropped one of the two weekend market days. The notebook showed it barely covered its costs.
3. He put his phone in the kitchen at 11 p.m. on work nights.
4. He moved the real monthly number, 410, into his family budget instead of the dream number, 600.

Three months later his side business was bringing in a bit more, around 480 a month, with fewer hours. It was not a miracle. It was the same man with the same stall. He just knew what was true now.

Try this: the three-line notebook

You do not need to run a business for this to help. It works for a job, a savings plan, a fitness goal, or anything where you think you know how things are going. Here is the template.

A few rules to keep it alive:

• Same time every day. Tie it to something you already do, like brushing your teeth.
• Paper or phone notes, not a new app. The fewer steps, the better.
• Missed a day? Fill it in tomorrow if you can remember. If not, leave it blank and move on.
• Be honest about the money. Write what is left after costs, not what you took in.

The weekly review: fifteen minutes on Sunday

Writing is only half of it. The real value comes when you read it back. Once a week, sit down with a pen and go through the last seven entries.

1. Add up the money line. Write the weekly total at the bottom of the page.
2. Circle your two best days. Look at what they have in common. Start time? Type of task? Sleep?
3. Mark your two worst days. Same question. What was different?
4. Compare with your guess. Before you add it up, guess the total. See how far off you were. This alone teaches a lot.
5. Pick one small change for next week, based on what you saw. Just one.

After four weeks, add up the four weekly totals. That is your real monthly number. Put it next to your spending. If you are not sure where the rest of your money goes, our post on where your money really goes walks through it, and the money leak calculator shows how small daily costs add up over a year. If you want to understand why tiny routines like this stick, our Atomic Habits summary explains the idea well.

The honest downsides

This is not magic. Six weeks of notes is a small sample. Some of Karim's patterns might have been luck, weather or a school holiday. The notebook points you at questions. It does not always give final answers.

It can also feel bad at first. Seeing that you make 410 and not 600 is not fun. Some people stop writing because the truth is uncomfortable. That is normal. The number was already 410. The notebook just stopped you from spending the other 190.

What this page cannot tell you

It cannot tell you what your own notebook will show. Your best days might follow late starts, or have nothing to do with time at all. It also cannot replace proper bookkeeping if you run a registered business. Your tax rules may ask for full records of income and costs, and three lines a day is not enough for that. This page is general information, not financial, tax or legal advice. If your side income is growing, talk to a qualified adviser about your country's rules.