Interface Incompatibility Among Successful Contributions: Why Parts That Each Work Can Fail When They Are Joined

This conceptual paper introduces Interface Incompatibility Among Successful Contributions, a mechanism in which separately successful contributions fail when they are connected because their formats, assumptions, schedules, or shared constraints do not match. Each contribution can meet its own standard while the assembled process fails at the point where the parts meet. The account assesses a failed joint effort by examining the compatibility and success of the assembled process rather than the local success of each contribution. The failed interface must be identified. A defective component, an ignored specification, or an unexplained appeal to emergence does not establish the mechanism. Evidence includes the standards each contributor worked to, the requirements at the interface, tests of the connected whole, and responsibility for the connection. The discussion connects the mechanism to David’s account of technical interrelatedness and examines the break of gauge at Albury, where the railway systems of New South Wales and Victoria met from 1883. Each railway operated successfully on its own gauge, but trains could not continue across the junction without passengers and freight being transferred. The mismatch lay in the distance between the rails rather than in the local operation of either network. Part of the Coordination and Dependence series within On Human Modeling, the paper examines how successful contributions fit together, who is responsible for their interfaces, and who bears the cost when they do not. Its framework can inform human–AI research on multi-agent systems, tool chains, shared data formats, and workflows in which locally successful components fail when combined.