The most important growth metric for most startups in the early days is understanding retention cohorts since this is often the best proxy for product/market fit. If you can retain users, you’ve created something valuable. Once you have a metric for validating product/market fit, I then would shift to the key growth metric which is a North Star Metric (NSM). Much like retention cohorts, the right NSM quantifies the growth of the aggregate value delivered to customers. Sustainable value growth makes sustainable revenue growth possible. The right NSM also gives context to all other metrics, experiments, and execution tasks.