Write personas from evidence

Supports: Developer, week 2 (Know the people): the persona sheets and the K/G rule. Time: about two and a half hours.

1. Why this matters

A persona is a short description of a typical person who uses or buys your product. Its job is not to be pretty. Its job is to settle arguments. When two people on your team disagree about a feature, the persona lets them ask: “Would Maya want this?” When an AI agent has to choose between two designs, a persona in its instructions turns a coin flip into a reasoned choice.

But a persona is only as good as the evidence behind it. A persona invented in a meeting is an opinion with a name and a stock photo. It feels helpful and quietly steers the product toward what the team already believes. NN/g puts the warning plainly: personas make users memorable, but they must be grounded in research, otherwise they mislead.

For a Product Development Manager (PDM), this lesson trains an essential habit: never state as fact what you only believe. The Dojo uses a simple device for that. Every line in a persona is marked K (known, with a source) or G (guess). Marking guesses does not make you look unsure. It shows you know the difference, and it tells you what to learn next.

What the PDM decides here

You decide	You may delegate to an agent	You verify	Other disciplines involved
Which patterns count as a persona, which lines are known and which are guesses	Formatting a sheet; checking for stereotypes and vague words; finding public statistics, with links	Every K line has a real source you can point to; no invented quotes	Design research, marketing, support, accessibility specialists

2. Key ideas

What goes in a persona

Keep it short. A useful persona answers six questions:

1. Who is she? Name (a placeholder), a few demographic facts that matter, and her situation.
2. What is she trying to do? The job, in her words.
3. What gets in the way? Her pains and workarounds.
4. How does she decide and pay? Who else is involved; what makes her say yes or stop.
5. How does she find and use things? Channels, devices, habits.
6. How do we know? Evidence: how many interviews, which data.

The Dojo persona template turns these into a sheet. Use it.

K and G: known and guess

Mark	Meaning	Needed
K	Known. You can point to an interview, a data point or a document.	A source tag, for example [C1, C3, C4]
G	Guess. A reasonable belief you have not checked.	A line in the “to learn” list

Rule: a persona may contain guesses, but never hidden guesses. If a line has no mark, mark it G.

Demographics: only what matters

Age, job and city are easy to write and often useless. Include a demographic fact only if it changes a decision. “28 years old” matters little. “Commutes by train for 40 minutes and buys two coffees a day” matters a lot. If a demographic detail could be a stereotype, such as gender, nationality or age assumptions, ask whether it came from evidence or from habit. Remove it if it is habit.

Behaviour and context beat labels

Describe what the person does and faces, not what category she falls into. “Millennial tech lover” tells you nothing. “Checks the app while standing in the queue, one-handed, with a bag on her shoulder” tells you where the button should be.

Archetypes and personas

If you only have patterns, not enough detail for a full persona, you can write an archetype: a short label and a few traits for a group you have seen repeating. NN/g has a short video on the difference. An archetype is a good step on the way to a persona. A persona is richer and needs more evidence.

Personas live

New evidence should change your personas. NN/g describes personas as living documents: design them so that updates are easy, and record the date and the reason for each change. A persona with a change log is a sign of a team that keeps learning.

Accessibility and inclusion

Real people include those who use screen readers, speak a second language, have low vision, use older phones or have slow connections. If your evidence shows such needs, put them in a persona. If your evidence shows none, that is not proof they do not exist. It may mean you did not talk to those people. Mark it as a gap.

3. Step by step

Step 1: Prepare the evidence

Gather your interview notes, your roles table from the last lesson, and any data you have (support messages, analytics, survey answers). Keep names out. You will refer to people by their codes.

Step 2: Draw an empathy map for each interview

For each interview, draw four boxes: says, thinks, does, feels. Fill them from your notes. Mark any box item that is only your guess. NN/g’s article on empathy mapping gives a quick explanation. This takes ten minutes per interview and shows you the gaps between what people say and what they do.

Step 3: Look for patterns

Lay the empathy maps side by side. Look for repeats in goals, in pains and in behaviour. Two or more people with the same pattern is the start of a persona. A pattern only one person shows is an outlier: note it, but do not build a persona on it yet.

Step 4: Fill the persona sheet

Use the template. For each line write the content, then mark it K or G. For each K, add the source codes, for example [C1, C3, C4]. Do not add a K line from a single person unless you say so: [C3 only].

Step 5: Write the one-page persona

When the sheet is done, write six to eight lines in plain words. Keep the placeholder name. Use real quotes in quotation marks, with the code. End with “How we know” and “What we still need to learn”.

Step 6: List what you do not know

Write the top five unknowns for each persona. For each unknown, write how you will learn it (an interview question, a data pull, a test). These go into your next round of conversations.

Step 7: Review and date

Ask one person to read the persona and say: “Is there anything here that sounds like you made it up?” Fix or mark those lines G. Add the date and a line Changes at the bottom.

4. Worked example: TrailMug

TrailMug is fictional. The people, quotes and numbers are illustrative. They show the shape, not a finding.

Persona sheet extract: Maya, the commuter

Line	Content	Mark	Source
Situation	Commutes by train 40 minutes, buys coffee twice a day	K	C1, C3, C4
Age	Late twenties to mid thirties	G	Based on three of five; no data
Job	“Get my coffee without a fuss and without feeling guilty”	K	C3
Pain	Used cup is dirty and leaks in the bag	K	C1, C3, C4
Workaround	Leaves cup at home; buys a throw-away one	K	C1, C3, C4, C5
Pays when	First month is free and cancelling is easy	G	Hint from C4 only
Finds things by	Search and word of mouth	G	No evidence yet
Uses	Phone, one-handed, in the queue	K	Observed in C3
Accessibility	Unknown	G	No one in the sample mentioned any

One-page persona (Maya):

Maya (placeholder name) commutes by train for about 40 minutes and buys
coffee twice a day. [K: C1, C3, C4]
She wants her coffee without a fuss and without feeling guilty. "I just
want to get on with my day." [C3]
What stops her: a used cup is dirty and leaks in the bag; she leaves it
at home and takes a throw-away cup. [K: C1, C3, C4, C5]
How we help: swap a used cup for a clean one at any partner cafe.
She may pay when the first month is free and cancelling is easy. [G]
Where she is: on her phone, one-handed, in the queue. [K: C3]
How we know: five interviews in November (fictional); behaviour seen in one.
Still to learn: does she pay? how does she find partner cafes? any
accessibility needs? what does a clean cup need to look like for her to trust it?
Changes: first version 2026-11-05.

Persona 2: Leo, the café owner is written the same way, from the three café interviews. His lines include “K: worries about hygiene rules [P1, P2]”, “K: lunch queue is the pressure point [P1, P3]” and “G: would pay for a monthly report on new customers”.

Barista note (archetype): one short archetype for the person who scans the cup, because the evidence is two observations and one interview. It is labelled an archetype and flagged as a persona to write after more evidence.

Look at what the example does. It has plenty of G marks. It names its unknowns. It does not claim an age range as fact. A teammate can use it today and knows exactly what to learn next.

5. Working with AI agents on this

Personas are the place where AI is most tempting and most dangerous. Models can write a smooth, detailed persona in ten seconds, with a name, a job, a hobby and a quote. All of it is made up. The Dojo rule is clear: no AI-invented personas, no invented quotes, no invented journey steps.

Delegate:

• Formatting: “Put my notes into this template. Do not add content that is not in my notes. Leave blank cells empty.”
• A stereotype check: “Read this persona. List any line that relies on a stereotype or assumption, and say why.”
• A vagueness check: “List words that two people could read differently.”
• Finding public statistics with sources, such as the number of commuters in a region, for you to verify and mark K only if you opened the source.
• A usage test. Give the finished persona to an agent and ask it to judge two design options as that persona, then compare with what you know. This tests whether the persona is specific enough to be useful. It does not prove which option is better.

Do yourself:

• Find the patterns and decide what is a persona.
• Mark K and G.
• Write the quotes from your notes, word for word.
• Decide what you still need to learn.

A brief you can adapt:

Here is a persona I wrote from interviews. Each line is marked K (known,
with source codes) or G (guess).
1. List every line that depends on a stereotype or an unstated assumption.
2. List every K line whose source codes look too few to support it
   (fewer than two people), without changing the mark.
3. List words that two readers could interpret differently.
Do not rewrite the persona. Do not add detail. If everything looks fine,
say so.

How to check the output. Compare each flagged line against the sheet. Remove any suggestion that adds new detail. When an agent says a K line has too few sources, check your notes. Maybe the mark should change to G.

Watch for flattery. Agents tend to praise what you give them. If a review comes back with no criticism at all, ask again with “What is the weakest line and why?”

Disclose. Add to the persona file: “AI use: formatting and stereotype check; I wrote the content and marks.”

Where this sits on the ladder. The agent skill of a manager climbs four rungs: use one agent, delegate whole tasks with a brief, orchestrate several sessions, and govern them with written policy, hooks and gates. This lesson sits on use and delegate. Checking a draft against your evidence is a task you hand over with a brief. A rule that a persona may not contain a fact without a source is policy, even when it is one line in your repo. The agent orchestration track covers the two upper rungs.

6. Common mistakes

• Inventing detail to make her feel real. A made-up hobby and a stock-photo name make a persona feel real and tell you nothing.
• Hiding guesses. Every unmarked line is a risk. Mark it G.
• Too many personas. Two to four is plenty. More will not be read.
• Personas from one person. One story is a case, not a pattern.
• Averages. A person who is “30 percent this and 70 percent that” does not exist. Describe a specific person instead.
• Stereotype shortcuts. Do not guess gender, age or tech skill from a job title.
• Writing it once and filing it. Date the persona and update it whenever you learn something.
• Letting an agent write quotes. Quotes come from real mouths only.

7. Practice: two to four personas

Deliverable: a folder people/personas/ in your git repo with:

1. One file per persona (maya.md, leo.md, and so on), each with: the filled sheet with K and G marks and source codes, the one-page persona, a “still to learn” list of five unknowns with a plan for each, and a Changes line with the date.
2. people/personas/README.md: how many interviews and data sources the personas came from, which gaps you know about (for example “no one using assistive technology”), and your AI-use line.

If your evidence is thin, write fewer personas and mark more lines G, or write archetypes instead. A short honest set is better than a long invented one.

Commit with a message such as Add personas with K/G marks.

Check: hand the personas to a friend with no context. Ask them to point to a line that sounds invented. Fix or re-mark it.

Stretch: run one more interview aimed at the biggest unknown. Update the persona, change the marks and record the date and reason in Changes.

8. Checklist

• Every line is marked K or G.
• Every K line has source codes.
• Quotes are word for word from my notes.
• No unexplained demographic detail.
• No stereotype guessed from a label.
• I listed at least five unknowns for each persona, with a plan.
• Accessibility and inclusion gaps are written down.
• The persona has a date and a Changes line.
• I recorded my AI use, and no AI invented any person or quote.

9. Further learning

Read NN/g’s article on personas and watch its two short videos on the basics of personas and on keeping them current. The archetypes video helps if your evidence is not yet rich enough for full personas. The Google UX Design Certificate video on storyboarding and wireframes shows empathy maps, personas and journey maps used together, and Figma’s design research guides add templates and methods. In the next lesson you will map the touch points and draw the journeys for your personas.