Resilience

Resilience is the capacity of a system to absorb disturbance and reorganize so as to retain essentially the same function, structure, and identity. It is distinct from both robustness (maintaining function without reorganizing) and stability (returning to the original state). A resilient system may be dramatically altered by a disturbance and still survive as a functioning system; a merely robust system resists alteration.

The concept originates in ecology — C.S. Holling's 1973 paper distinguished engineering resilience (how fast a system returns to equilibrium) from ecological resilience (how large a disturbance a system can absorb before flipping to an alternative state). The distinction matters: engineering resilience is optimized by efficiency; ecological resilience is maintained by redundancy, diversity, and feedback richness — properties that look wasteful from an efficiency standpoint and are therefore systematically destroyed by optimization processes. This is why highly optimized systems are fragile: they have traded resilience for efficiency, a trade that is invisible until the disturbance arrives.