The rise of generative AI challenges the traditional copyright system centered on natural persons. Works created by natural persons through prompt adjustments and output selections often face difficulties in assessing human contribution due to algorithmic black boxes. Judicial practice recognizes the copyrightability of such AI-assisted outputs but fails to clarify the depth of human involvement via prompts. This paper focuses on the normative meaning of “substantial contribution,” correcting deviations in the sweat-of-the-brow doctrine and actual control theory. It emphasizes the role of human intellectual input in shaping original expression and advocates a process-oriented review approach. By analyzing creative nodes, causal chains, and contribution levels, it identifies human creativity beyond technical black boxes, balancing technological innovation with the anthropocentric values of copyright law.