24/7 large systems break at 3am when the most-tired person takes pager. 500M daily events, 99.95% SLA — if a known failure type each time wakes a human, remembers procedure, patches console: average pager delay alone is 6 minutes. SLA dies. Mature ops sets one goal: "80% of known failure types auto-recover before anyone wakes." Today: that goal's structure — EventBridge as signal-intake, Step Functions wrapping Runbook (retry, audit), Incident Manager pulling in humans when auto-recovery breaks. And: where auto-response fails dangerously. Reliability engineering, idempotency theory.