The AI-Month Fallacy

The Brooks volume proposes that the man-month's mythical status finds its contemporary analog in the AI-month: the managerial assumption that an AI tool can replace a human developer on a month-for-month basis, enabling headcount reduction without loss of capability. The AI-month is mythical for different reasons than the original man-month. The man-month was mythical because adding people added communication overhead that consumed the additional capacity. The AI-month is mythical because substituting AI for a human developer eliminates not just the person's implementation capacity but also the person's embodied understanding of the system, the person's capacity to catch errors through orthogonal expertise, the person's institutional memory, and the person's capacity to develop into a more senior contributor over time. The substitution appears equal on the ledger of hours; it is deeply unequal on the ledger of capabilities.