Still, that engineer (if its engineer's fault) is extremely unlikely to make that issue again. IMHO, the problem is systemic in that why the system allows such

Still, that engineer (if its engineer's fault) is extremely unlikely to make that issue again. IMHO, the problem is systemic in that why the system allows such errors (if its human error) to happen. Given Google's scale I think a lot of the generally known scenarios are covered and what you see is tens of services interacting in not obvious ways. Those unobvious scenarios manifest in situations like this.