Deep beneath the Atlantic, Cold War submarines hunted one another through the dark. A trace of engine noise, the vibration of a pump, the rhythm of a propeller could betray a vessel that was otherwise invisible. Analysts learned to recognize these acoustic signatures and infer what was moving through the water. I became fascinated by the idea that a complex system reveals itself through the pattern of its operation. A company, I thought, might do the same through the decisions it makes.