Diverse Redundancy
TL;DR
Three identical backups sharing the same bug provide no real redundancy. Boeing's 737 MAX MCAS relied on a single sensor; SpaceX's Falcon 9 uses three different computers from different manufacturers running different software.
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Instead of duplicating identical systems, use different systems that accomplish the same function through different means, protecting against common-mode failures.
Business Application of Diverse Redundancy
Nestlé's multi-origin coffee sourcing uses different farming systems, weather patterns, and political contexts - providing redundancy unlikely to fail simultaneously. SpaceX's Falcon 9 uses three independent computers from different manufacturers running different software implementations, protecting against software bugs affecting all copies.