Behavioural round: build your story bank

Many companies have a round that is not about code or design. The interviewer asks: "Tell me about a time you disagreed with a teammate." This is the behavioural round. The interviewer cannot watch you work, so they listen to one real event from your past and decide how you would work with them.

A weak answer has a long background, says "we" all the time and has no result. A strong answer is short and clear. It says what the problem was, what you did and what changed, with a number. "I would do X" is only a promise. A real event is proof.

Most people have good stories. They fail because they choose one while they are speaking. This lesson shows you how to choose six stories once, write them down and use them for many questions.

Think of packing a bag the night before a trip. You choose the things when you are calm, not at the bus stop while the bus is moving. A story bank is that bag: a small set of true stories from your work, chosen and practised before the interview.

What the round tests

The interviewer wants to learn four things:

• what you did yourself,
• how you decide when things are not clear,
• how you work with other people,
• how you learn, especially from what went wrong.

They ask about the past. "What would you do if..." tests what you think you would do. "Tell me about a time..." tests what you did.

Tradeoff's behavioural mock works like this. It asks three questions, each on a different theme, and asks more about one real story for each. If your answer is only "I would" or "I usually", it often asks for one real time. The report then scores six things: ownership (you are responsible for the result), impact and results, judgement and trade-offs, collaboration and influence, learning and knowing your weak points, and communication.

The shape of an answer: STAR

A good answer takes about two minutes and has four parts. Their first letters make the word STAR.

1. Situation. Where and when, and what could go wrong. One or two sentences.
2. Task. What your job was in it. One sentence.
3. Action. What you did, step by step, in order. Use "I". This is the longest part.
4. Result. What changed, with a number or a clear before and after. Add one sentence on what you learned.

How long is each part? Assumption: you speak at a calm 120 words a minute. Two minutes is then 2 x 120 = 240 words. Our suggestion, not an official rule: situation and task together get a quarter, 60 words. Action gets half, which is 120 words. Result gets a quarter, which is 60 words. Action is the longest because it shows you.

A result needs a number or a clear before and after

Choose the result in this order:

1. A metric. Time, money, errors or users. For example: "Users charged twice fell from 2,300 to 0."
2. If you have no metric, use something else that is true. Time saved ("the weekly report took 3 hours and now takes 20 minutes"). Fewer errors ("support tickets fell from 12 a week to 3"). People helped ("5 new joiners used the guide in their first month"). A decision made ("the team chose option B and shipped one week earlier"). All these figures are examples.

Always say how you know the number. If you did not measure it, say so: "I did not measure it. I know it worked because the complaints stopped." This is better than a number you made up.

The story bank: six stories, many questions

Choose six real stories from the last two or three years. Cover these six:

1. a project you owned,
2. a hard problem,
3. a mistake,
4. a disagreement,
5. a tight deadline,
6. learning something new.

For a more senior role, also prepare two more. One is a project where the goal was unclear. The other is a time you changed what other people did without being their manager. That is called influence.

Tradeoff's mock has 11 question themes:

• ownership,
• a hard problem,
• a mistake and what you learned,
• a disagreement,
• a tight deadline,
• learning something fast,
• an unclear goal,
• influence without authority,
• helping others grow,
• saying no,
• technical direction.

You do not need 11 stories. One story can answer three or four themes, because the same facts can be told with a different focus. A story about a hard bug can answer three questions:

• "a hard problem": focus on how you found the cause,
• "ownership": focus on why the fix was yours,
• "a mistake": focus on what the team missed.

So make a story map: a table that shows which themes each story can answer. A theme with no story is a gap. Fill it with a new story.

In one round, do not use the same story for two questions. Tradeoff's mock asks you to use a different story for each question. So have at least three ready. Six gives you a choice.

How to write one story

1. List the facts. Write the facts only, not sentences: dates, team size, numbers, tools, who did what, what you decided, what else you could have done, what changed.
2. Write a short version. About 120 words in STAR order. This is the one-minute core, also our suggestion.
3. Say it aloud and time it. Add the one or two details that make it real, up to about 240 words. Cut anything that is background.
4. Keep a one-page fact sheet. For each story, write the numbers, dates, tool names and who did what. Then the numbers are the same every time. A number that changes makes the interviewer doubt all of them.

Freshers and career changers

You do not need a job to have stories. A college project, an internship, a hackathon, open-source work or a part-time job all count. Say what was yours: "My team had four people. I wrote the login and the database part, and I wrote the test." The interviewer wants your part.

When no story fits

Sometimes you have no story for a question. Say so, and then use the closest real one: "I have not had a disagreement with a manager. The closest is one with a teammate about API field names." Never invent a story. A follow-up question finds it quickly, and then the interviewer doubts everything else you said.

How the interviewer asks more

The interviewer will not stop at your first answer. Expect: What did you personally do? What was the number, and how do you know? How many people worked on it? How long did it take? What would you change? Under each story, write five such questions and your answers. In Tradeoff's mock the interviewer always asks what you did and what the result was.

Five common mistakes

• A long background. Two sentences are enough.
• No result. The answer stops at "and then we released it".
• Only "we". The interviewer cannot tell your part.
• A number you cannot explain. Percent of what? Measured how?
• A script that you have memorised. It breaks when the interviewer asks something in between.

All people and companies here are made up. Meera is an SDE-2 (second engineer level) at a made-up bill-payment app. Salary day is the first day of the month, when many people get their salary and pay bills at the same time. These are Assumptions:

• Her team has 5 engineers.
• On salary day a payment sometimes took too long, so the app tried it again, and the bank took the money twice.
• 2,300 users were charged twice. The team saw it only after 45 minutes.
• Meera found the cause in the logs: the same payment was sent twice.
• She wrote the fix. It gives every payment one unique number, so a second try with the same number is ignored (lesson 89, doing it twice is safe).
• She also wrote a test that sends one payment twice. A teammate reviewed the fix.
• She added an alert for payments that look doubled.
• In the next month's run, duplicate charges fell to 0. Refunds were finished in 2 days.

The story told badly:

"So, our company was started in 2019, and we have many services. My team handles payments and many other things, and last year, around the festival season, we had some issues. We looked into it, and we fixed it. Now it is working well."

The same story told well:

"Last year, on salary day, our app charged 2,300 users twice. [Situation] I owned the payment service, so finding the cause was my job. [Task] I compared the payment numbers in the logs and saw that one payment was sent twice after a slow reply from the bank. I wrote a fix that gives each payment one unique number, so a second try is ignored. I wrote a test that sends the same payment twice. I also asked a teammate to review it before the next salary day. [Action] In the next month's run, duplicate charges fell from 2,300 users to 0. We finished all refunds in 2 days. I also added an alert, so we now see such a problem in minutes. I learned that every job that moves money needs an alert. [Result]" The tags in square brackets are for you. Do not say them.

This answers the predict box. Task, action and result are missing or weak. The words "we fixed it" hide the action, and "working well" hides the result.

Now the story map. Meera's six stories and the themes each can answer:

The double-charge story answers three themes. Ownership appears in four rows. Two themes have no story yet: helping others grow, and technical direction. For a Senior role, Meera would add a story for helping others grow.

• A prepared story bank solves choosing a story while you speak, and it keeps your numbers the same each time. It costs a few hours of work and a risk of sounding memorised. I would change the bank when a story is about three years old, or when a theme has no story.
• A two-minute answer solves the problem of a bored interviewer, and it lets them choose what to ask next. It costs detail, which I keep in my fact sheet. I would give a longer answer only when the interviewer asks.

"I need one perfect story that I can use for every question." One story cannot answer every question. Each question looks at a different part: a disagreement looks at how you treat people, and a mistake looks at how you learn. Also, an interviewer who hears the same story twice learns less about you. Six stories with a different focus work better.

"Only big successes make good stories." A small project with a clear result and your own actions beats a big project. In the big project you may not be able to say what you did. Some questions ask directly about a mistake. A mistake that you fixed and prevented again is a good story.

"I should learn the story word for word." A memorised script breaks when the interviewer asks a question in the middle. Learn the facts and the order of the four parts. Let the words change each time.

1. Name the four parts of STAR in order. Which part should be the longest?
2. Your story has 330 words. You speak at 120 words a minute. How long does it take? How many words must you cut to fit in 2 minutes? If the action part should be half of the final story, how many words is that?
3. The interviewer asks: "Tell me about a time you disagreed with your manager." You have never done that. You once disagreed with a teammate about how to name the fields of an API. What do you do?