Long-term tirzepatide treatment produces substantial weight loss that reliably decelerates and plateaus. A recent modeling analysis attributes this plateau to a progressive narrowing of the energy gap between intake and expenditure [1]. That explanation cannot be sustained. The model assigns a fixed tissue energy density of 7170 kcal/kg to all weight change, collapsing fat, lean tissue, glycogen and water into a single caloric equivalent. More critically, energy intake is not measured; it is calculated as the residual required to reconcile modeled expenditure with observed weight change. When weight change approaches zero, intake and expenditure must converge by definition. The reported convergence is therefore tautological. The same decelerating trajectory is the geometric signature expected when net mass outflow scales with retained mass. Once the body is treated as a mass reservoir whose clearance rate depends on the mass it still contains, the square-root relationship follows by mathematical necessity. No adaptive thermogenesis or other auxiliary construct is required. The plateau is the predictable behavior of a physical system, not evidence of emerging physiologic resistance.