Why building for one person beats building for everyone

Most founders want to build for everyone. It feels ambitious, it sounds good in a pitch, and it makes the market size slide look impressive.

But building for everyone is the fastest way to build for no one.

To show why identifying a target user matters so much, I'll share an extreme case: when I built a French language app for exactly one person — my dad.

Why I started building

My dad has been studying French for years. He recently started using Duolingo to augment his reading and conversation classes, but he complained it wasn't getting him to the level he wanted. His goal was to reach C1 proficiency in French — a level where you can debate, write persuasively, and understand cultural nuance.

More importantly, he wanted to feel confident speaking with native French speakers, to understand expressions and colloquial language, and to sound natural in conversation.

When I dug into where Duolingo wasn't delivering, he mentioned a few fronts:

• It felt too simplistic for an advanced learner.
• It didn't reinforce prior lessons, so he often forgot what he'd learned.
• It wasn't preparing him for fast-paced, real conversations.

But there were things he loved about the app: the short lessons and the mix of listening, writing, and speaking.

Knowing my target user

Because I knew my "customer" so well, I had a detailed profile to design around:

• Baseline: B2 level.
• Goal: master B2 and work toward C1.
• Motivation: confidence in real conversations with native speakers.
• Learning style: very visual.
• Preferences: short lessons, structured "homework," a balance of listening, writing, and speaking.

This clarity was my north star. Instead of guessing at what "French learners" in general might want, I could zero in on what mattered to him.

The first build

I researched what it actually takes to move from B2 → C1: advanced grammar, oral fluency, debate, and cultural nuance.

With that, I built an MVP:

• Debate tools powered by Claude's API.
• Pronunciation exercises.
• Cultural/linguistic nuance gleaning from real-world content.

When I put it in front of him, the results were instant.

He was enthralled by the debate feature. I could barely pull him away from the computer. He has spent hours debating with Claude!

But the feedback on the pronunciation and written modules wasn't detailed enough, rendering it useless to him.

And I hadn't built out a module to tackle oral conversation because I was struggling with the technology. But my dad was disappointed to see that wasn't there, reinforcing how important that was to him.

Iterating on feedback

That feedback was gold. And because my target user was so specific, the signals were crystal clear.

So I went back to research: what tools support advanced oral conversation? How do you deliver feedback that is both encouraging and appropriately challenging for a C1 learner?

I used Claude's API to validate the linguistic accuracy while my dad validated the user experience. I leaned on him to be my design partner — not just a tester, but someone who gave continuous feedback on what worked, what didn't, and what was missing.

Having a true design partner is invaluable. For startups, finding even a handful of these users early on can save months of wasted effort and give you clarity no research report will match.

The outcome

The result was a tool my dad actually enjoys, uses regularly and talks about with his friends. And really, what more could I want?

The lesson for founders

This started as a side project for fun — but turned into a vivid case study in why identifying a target user is so critical.

If I hadn't known my dad's baseline, goals, and preferences so well, I could have wasted weeks overbuilding features that didn't matter. Instead, I built what mattered for him, learned from his feedback, and iterated quickly.

That's the power of a clear target user:

• You know what really matters vs. what's just noise.
• You get focused, actionable feedback.
• You can prioritize ruthlessly and iterate with speed.

Furthermore, your first target users should be your design partners. They'll push your product in ways you can't predict, highlight what's missing, and validate what truly resonates.

You don't need to launch with a massive audience. Start small, with a clear user in mind, listen deeply and iterate with intention. That's how good products are built.