A good infra architecture has the “blast radius” of any issue confined to only part of your infra fleet. Avoiding the global outage.
Think of it like a navy ship. When a mussel breaches the hull, the ship is designed to contain the leak in a single section. Avoiding the entire ship sinking. Similar pattern is desired in your service and compute infrastructure.
The outage google just faced is equivalent to a single missel taking down an entire navy fleet.