Ask HN: How do you build, nurture, and grow a Platform-as-a-Service business?

There are many excellent platform-as-a-service (PAAS) business that have grown from a simple idea done well. Are there any personal experiences from individuals who have led, participated in, observed, competed against such a company (companies like Stripe or Twilio or ...)? Are there any good resources to learn from? What are key concepts to focus upon? Thanks!