It’s Black Friday. Checkout latency is spiking. Your on-call engineer pulls up the dashboard and starts working through the list. Is it a regional issue? No, all regions look fine. A payment provider? Stripe, PayPal, Apple Pay all nominal. A bad deployment? Nothing shipped in the last six hours. All your infrastructure dashboards are showing green. But customers are complaining. Checkout is slow, carts are being abandoned and revenue is draining away.