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Doctor Market Fit

Ultimate Guide to Interviews #1: Build a customer theory

Take off your founder hat, put on your anthropologist hat

Jeroen Coelen's avatar
Jeroen Coelen
Oct 15, 2025
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Today marks the start of a series of posts on how to do proper customer interviews, either solution or problem focused.

It’s based on my experience with hundreds of founders I’ve trained on doing interviews, and of course my own experience in doing interviews.

Happy reading!
Cheers, Jeroen

Table of Contents

  1. Goal: Build a customer theory ⬅️ This post

  2. Starting the interview: Keep your baby in your bag

  3. Don’t open with problem search

  4. Finding emotions and purpose

  5. Identify the big picture of your customer

  6. Understand criteria of success via competition

  7. Using the film-reel technique to get detailed explanations

  8. Six techniques on how to wiggle out extra information

  9. Getting your baby out of the bag

  10. Crafting your customer theory

Note: I will not touch upon how to find people to talk to. That’s a different guide. For the current interview guide, I assume you have a call or meeting scheduled.

Chapter 1: Build a customer theory

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