Thank-You Letters: The Habit That Turns a Conversation Into a Relationship

By Kasper-Tanakrit Sermsuksan · Global Venture I: Playbook · Block A

You are here: A-07 · Block A · Orientation & Mindset · article 7 of 10 · Form A+B · Next: A-08 The ASEAN Friend Interview

In short: A thank-you letter after a customer or founder interview is a short, specific email that thanks the person, names exactly what you learned, and says what you will do next. That is what turns a conversation into a relationship. It also forces you to structure your own learning — and it only works if it is genuine. Send it within 24 hours, by email if you can, and attach the photo if you took one together.

จดหมายขอบคุณคืออีเมลสั้น ๆ ที่เราส่งหลังมีคนสละเวลามาคุยด้วย เวลาเขียนจดหมายขอบคุณ ให้บอกให้ชัดว่าเราได้เรียนรู้อะไรจากเขา และจะเอาไปทำอะไรต่อ ไม่ใช่เขียนแค่ว่า "ขอบคุณที่สละเวลา"

Try it in 10 minutes: Think of the last person who gave you their time — a teacher, a boss, a stranger who helped. Write them three sentences: one thing they said, in their words; what it changed for you; and what you will do next because of it. Read it out loud. If it could be sent to anyone else, rewrite it until it couldn't.

The first business owner I ever interviewed sent me a text from an unknown number while I was on a beach with friends, roasting marshmallows.

"I'm free on Tuesday at noon."

It was my classmate Feli's mother. She was one of the first people to open a sushi restaurant in Mexico City, and she grew it into a chain across Latin America. I borrowed a friend's car (on the condition that I drive him to his own job interview the same day) and sat with her for almost an hour.

At the end, nervous, I asked for a selfie for my class assignment. She laughed, posed, and then offered to introduce me to her other entrepreneur friends. I had not even asked.¹

I walked out thinking I was lucky. I was. But I have since learned that the hour is only half of it.

The next 24 hours decide what that hour becomes.

Why write a thank-you letter at all?

Because "thanks for your time" is forgotten by lunch.

A note that says "what you said about hiring your first employee changed how I am thinking about my co-founder conversation next week" is remembered for years.

A real thank-you letter does three jobs.

1. It builds the relationship

The founders, customers, mentors and speakers who give you an hour are not a list of contacts. They are the start of your network.

In my experience, most founders never hear again from the students who interviewed them. The few who write back — and later send an update — move into a different box in that founder's head. Not "a student." Someone who is actually building.

To some of the people who helped me most, I wrote handwritten letters. Some of them still keep those letters today. Many became my great mentors.

Some of the people you thank this year will be the ones who pick up the phone for you in three years. See How to Build a Global Network That Actually Lasts.

2. It shows you what you learned

You cannot write a specific thank-you without deciding what you learned. That is the hidden purpose of writing it.

Within 24 hours, you have to name one or two things that changed your thinking, in plain words, and say what you will do about them. It is a small reflection on one conversation, while it is still warm.

If you sit down to write and cannot name anything, that tells you something too. Go back to your notes first.

3. It has to be genuine

People can smell a template. If your letter could go to anyone, it means nothing to the person who gets it.

Use their words. Mention the moment that surprised you. Say what you will actually do. If the honest answer is "you made me doubt my idea," say that — kindly. To a founder, that is worth more than flattery.

This is not about manners. It is about respect. Someone with no reason to help you chose to. Show them it mattered.

Who should get a thank-you letter?

• Every person who gives you an interview: founders, potential customers, experts, friends who tell you how their market works.
• Guest speakers, site-visit hosts and practitioners who give their time to your class or your team.
• Anyone who gives you a real introduction, a pitch meeting or feedback on your venture.

How should you send it?

• Email, if you can. A quick "thank you" on LINE or a DM right after the meeting is a nice touch. But a proper email shows more commitment. It is a record, it travels well inside organizations, and it is the habit you will need with funders and partners.
• Within 24 hours of the conversation, while you still remember the details.
• One from each person who was there. If two of you did the interview, each of you writes your own letter, in your own words. Two people rarely learn the same thing from the same hour.
• Attach the photo if you took one together. People like seeing the moment again, and it helps them remember who you are.
• Language is your call. I recommend writing in the language you spoke in. A conversation in Thai usually deserves a Thai letter, with the politeness the relationship calls for; an English conversation, an English letter. Sounding like yourself matters more than the language.
• Handwritten, for the people who changed something for you. It takes longer. That is the point.

✦ If you are doing this as part of Global Venture I: Playbook

Send it by email within 24 hours and CC kasper@seabridge.space — not BCC. Many of the founders and friends you will meet are people I know, some of them my friends and long-time connections, and I like to know who you met and how it went. One letter from each group member who took part. The CC is also your proof of submission. More in the course note at the end of this article.

How do you write a thank-you letter after an interview?

This is for founder, customer and expert interviews — not job interviews. (If you came here after a job interview, most of it still applies: be specific, be quick, be genuine.)

1. A subject line that says what it is. "Thank you — our conversation on [topic], [date]".
2. Thank them for something specific. Their time, yes. But name the thing they gave you: a story, a number, an introduction.
3. Name what you learned. One or two points, in their words where you can. This is the heart of the letter.
4. Say what you will do with it. The change to your idea, the next interview, the test you will run.
5. Give something back, if you can. A short summary of your findings, an article they would like, an introduction.
6. Keep the door open. Tell them you will send an update. Then actually do it, in about three months.
7. Keep it short. 120–200 words. Read it out loud once before you send it.

Do not worry if your first one feels stiff. When I was paired with my first real mentor, Terri, at USC, I emailed her before we had even met. Probably too formal. Probably three drafts.¹ She still met me regularly for coffee and lunch, and became the mentor who changed my career more than anyone. Send the stiff one. Just send it.

What about a thank-you letter after an informational interview?

An informational interview is a conversation where you ask someone about their work, their field or their path — not for a job. Most founder and customer interviews are this kind of conversation, so everything on this page applies.

The difference from a job-interview thank-you is the goal. After a job interview, you remind someone why they should hire you. After an informational interview, you show them what their time changed, and you keep the door open. Be specific, send it within a day, and never turn it into a request for a job they did not offer.

What does a good thank-you letter look like?

Here are two examples I wrote for this article. Same interview, very different letters.

Weak

Subject: Thank you

Dear Khun Somchai,

Thank you very much for your time and for sharing your valuable experience. It was very helpful for our project. We learned a lot. We wish you continued success.

Best regards,
Team 4

Strong

Subject: Thank you — your bakery's first year, 12 Feb

Dear Khun Somchai,

Thank you for giving me an hour on a Saturday, your busiest day.

Two things you said changed my plan. First, that your best customers came from the office building next door, not from social media — I had assumed the opposite. Second, that you tested every new product as a free sample before you put it on the menu.

So this week my team and I will stop planning an Instagram launch. Instead, we will offer free samples in two office buildings near campus, and count how many people come back.

I will send you what we find by May. If it is useful, I would be happy to share our short customer summary with you too.

With thanks,
[Your name], Chulalongkorn University

The weak letter could go to anyone, from anyone. The strong one could only go to Khun Somchai, from one person who was in the room.

That is the test. (If you are in my course, it is also the test I use when I read yours.)

Why keep a log of who helped you?

Because in a year you will not remember. Start a simple thank-you log now, with your first interview:

• Example: bakery owner, Samyan — Date we met: 12 Feb — What they taught me (one line): Best customers came from the office next door — What I promised: Send sample-test results — Follow-up due: May

After a few months, that log becomes your network list. It also shows you something about yourself: how many people helped you get here. Most students are surprised by the number.

Can I use AI to write my thank-you letters?

You can use AI to check grammar or tone. You cannot use it to decide what you learned. That part is yours. A thank-you letter is a reflection with a stamp on it. If a machine wrote it, it is not genuine, and the person will feel that.

Reality check

If you are doing many interviews, that is a lot of letters. After a few weeks you will be tempted to copy last week's letter and change the name. Please don't. Write it the same day, while you still remember the details. It takes ten minutes then and thirty minutes later.

It can also feel awkward to write to someone senior. That is normal. I felt it too. They were students once, and most of them remember who wrote back.

If you are struggling at this stage, you are like most people. It means you are doing the real work.

Frequently asked questions

What should a thank-you letter after an interview say?
Thank them for something specific, name one or two things you learned (in their words where you can), say what you will do next, and offer to send an update.

How soon should you send a thank-you letter?
Within 24 hours, while the details are fresh.

If we interviewed as a group, do we each send one?
I recommend it. Each person who took part writes their own letter, in their own words. (In Global Venture I, it is required.)

Is a LINE message or DM enough?
A quick note right after is a nice touch. But email shows more commitment: it is a record, it works across organizations, and it is how you will write to funders and partners.

Should I attach a photo?
Yes, if you took one together. It helps them remember you.

What if the interview did not go well?
Thank them anyway, and be honest about what you learned — even if it was that your idea needs to change.

Do I need to follow up after the thank-you?
Yes, if you promised to. Send an update in about three months: what you tried and how their advice helped.

Before you go — advice from last year's class. When I asked the 2025 class what the next cohort should know, one student wrote:

"Try reaching out, even to a stranger. The worst thing they can say is no. Just keep going. It takes a lot of time — the weekly forms, the thank-you letters to guest speakers, the final project — but the lessons you get are very valuable."
— CEDT student, 2025 (lightly edited)

I agree with every word.

✦ A Note for Global Venture I Students · Block A: Orientation & Mindset · Form A+B

Thank-you letters are 5% of your final grade (an individual component). They go by email within 24 hours, with kasper@seabridge.space in CC (not BCC) — one from each group member who took part. Write your reflections in your own words; if you used AI, say what for in the form's "AI used for:" field. Your first one follows your first entrepreneur interview, in Block A. Every interview and guest talk after that gets one too.

Do this before class:

1. Draft the skeleton of your letter for entrepreneur interview #1 now, using the seven steps. Fill in the details within 24 hours of the interview.
2. Start your thank-you log (the table above), with a follow-up date for each person.
3. In your Book Log, when you log Chapters 5–6, add one line: what did the founder's offer of introductions teach you about following up?

Pre-class check (in Form A+B):

1. Name the three jobs a thank-you letter does.
2. How, how soon, and by whom is a thank-you letter sent if you interviewed as a group?
3. Write the one sentence you plan to put in your first letter that names exactly what you learned (you can update it after the interview).

Your progress: Customer readiness to level 3 — interviewees who stay reachable for follow-up questions and your first tests. How we measure progress

Skills you practice: Empathy and active listening · motivation and self-awareness · learning through experience · mobilizing others.

Based on the KTH Innovation Readiness Level™ by KTH Innovation, licensed CC BY-NC-SA 4.0 (kthinnovationreadinesslevel.com).

Keep reading

• The ASEAN Friend Interview — next in Block A
• The Entrepreneur Interview — the conversation the letter follows
• Why We Ask You to Do 12 Interviews — and Why Only Five Are Customers — why the relationship is the asset
• How to Build a Global Network That Actually Lasts — what to do with your log after the course

All articles in Block A · Orientation & Mindset

• A-01 The Story Behind SEA Bridge
• A-02 Can Entrepreneurship Be Taught?
• A-03 SEA Bridge: The Cross-Border Venture Studio
• A-04 Should You Start a Company?
• A-05 About Global Venture I: Playbook
• A-06 The Entrepreneur Interview
• A-07 Thank-You Letters (you are here)
• A-08 The ASEAN Friend Interview
• A-09 How to Choose a Startup Idea
• A-10 How to Keep a Startup Journal

References

1. Sermsuksan, K.-T. (2023). The Startup Mindset [in Thai], Chapters 5, 6 and 28. Wish Publishing (สำนักพิมพ์วิช). English: the author's own translation, not yet published.

Further reading

• Grant, A. (2013). Give and take: A revolutionary approach to success. Viking.
• Emmons, R. A. (2007). Thanks! How the new science of gratitude can make you happier. Houghton Mifflin.

About the author: Kasper-Tanakrit Sermsuksan is the Founder of SEA Bridge and a Visiting Lecturer in Computer Engineering and Digital Technology at Chulalongkorn University's Faculty of Engineering. Learn more →