Active uniques were high, the amount of time people spent on the site was continuing to grow, and new accounts were being created at a rate faster than accounts were being closed. I shook my head; I didn’t think that was enough. A few months later, the site started to unravel.
Sounds a lot like the way ecosystems collapse. At first nothing seems amiss, maybe a slow decline, but hardly worrying. Time passes, and you start to think nothing bad will happen after all. Then an inflection point is reached, and catastrophic failure ensues in an extremely short time. And there's no going back after that.