This technical note maps heat generation and thermal trapping across the full pick-and-place cycle at the joint level and identifies the distal thermal trap as the governing failure mode in continuous-duty humanoid hands. It defines the worst-case sustained load condition (grip hold with micro-correction), explains why distal joints reach thermal instability first, and establishes proximal actuation with passive distal structures as a thermodynamic requirement rather than a design preference. The document provides a deployment-oriented architectural doctrine that can be used for direct comparison of existing and proposed hand systems.