What is robust systems?

Robust systems is a concept in personal epistemology: Multiple paths between important nodes make a system more robust.

Example: The Space Shuttle's flight computer system used five General-Purpose Computers, four running identical software in lock-step synchronization and one backup running independently written code. At the end of every clock cycle, the four primary computers voted on the correct output. If one computer failed, the remaining three continued voting. If two failed, the remaining two could still cross-check. If three failed, the independently programmed fifth computer took over. NASA designed the system to a 'Fail Operational, Fail Operational, Fail Safe' criterion — meaning it had to remain fully operational after any single failure, fully operational after any second failure, and still land safely after most kinds of third failure. The redundant relationships between computers meant that no single hardware failure — or even two — could kill the crew. The system didn't just tolerate failure. It expected it.

This concept is part of Phase 13 (Relationship Mapping) in the How to Think curriculum, which builds the epistemic infrastructure for relationship mapping.