Building the universal integration layer for modern products and raising a Series A from GV with Romain Sestier & Guillaume Lebedel, Co-Founders @ StackOne

Riding UnicornsMay 28, 202547 min

StackOne co-founders Romain Sestier and Guillaume Lebedel share hard-won lessons from building their universal integration layer startup and securing $20M in Series A funding from GV. Their contrarian approach—deliberately turning down revenue from wrong-fit customers and embracing unglamorous sales work like cold outreach and customer visits—challenges conventional startup wisdom about growth at all costs.

Key takeaways

  • Saying no to revenue from wrong customers is often more valuable than chasing any available dollar, especially in early-stage product development.
  • The best sales leads frequently come after the fourth unanswered follow-up, making persistence in outreach a crucial competitive advantage.
  • Co-founder relationship quality should be prioritized above product-market fit or fundraising strategy when starting a company.
  • Embrace the unglamorous sales work others avoid—webinars, travel, customer visits—as these create defensible competitive moats.
  • Venture funding fundamentally changes execution pressure, transforming every decision into a billion-dollar validation exercise.

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