Why high signup numbers are the biggest trap for early-stage SaaS

There is a dangerous illusion in watching your registration counter go up every morning when nobody is actually sticking around to use the product long-term. We realized our leaky bucket was wasting weeks of engineering effort on acquisition channels that brought in zero active users. Once we tied our team's goals to activation milestones instead of raw signups, everything changed. If you went through this same wakeup call, what specific metric finally forced your startup to focus on activation over volume?