Note 05 · systems
Fail-closed is different from fast
When execution has real consequences, uncertainty must reduce authority rather than trigger action.
Most latency-driven systems are designed so uncertainty speeds things up. If you do not know what is happening, you act more aggressively before the window closes. That is correct for some systems.
It is the opposite of correct for systems that move real money against real counterparties. There, uncertainty must reduce authority. The lane must disarm, the lock must hold, the executor must refuse to sign, the operator must be told.
Fail-closed is not slow. Fail-closed is fast at refusing to do the wrong thing.