Synchronized demand is the moment a large cohort of clients acts almost together. In a service with capacity $\mu$ requests per second and background load $\lambda_0$, the usable headroom is $H = \mu - \lambda_0 > 0$. When $M$ clients align—after a cache expiry, at a cron boundary, or as a service returns from an outage—the bucketed arrival rate can exceed $H$ by large factors. Queues form, timeouts propagate, retries synchronize, and a minor disturbance becomes a major incident. The task is to ...