" Two examples illustrate the redundancy principle. First, when a virtual machine fails in a cloud-based system, an identical instance is started automatically. Second, a critically important system should have at least one secondary backup system that runs in parallel with the primary system to ensure a safe fallback. Leading up to the next principle, we note that the secondary system should differ from the primary system to avoid both failing for the same reasons. "

― , Anti-Fragile ICT Systems