Index Ventures defines Product-Market Fit (PMF) not as a binary moment, but as a continuous process of shedding 'drag'. The framework identifies the three signals of true PMF: exponential organic growth (word of mouth), flattening retention curves (users stop churning), and unit economics that work at scale. It warns against 'False PMF' driven by paid acquisition or hype, and provides a roadmap for the transition from 'Founder-led Sales' to a scalable Go-To-Market machine.

PMF is the only thing that matters for a Series A. This guide prevents founders from scaling prematurely—the #1 killer of startups. It forces a rigorous audit of customer love versus bought attention. If you can't prove retention cohorts flatten out, you don't have a business, you have a leaky bucket. This framework is the benchmark top-tier VCs use to judge readiness for scale.