Why Excel Gantt Charts Fail: A Structural Analysis of Unidirectional Causality and Architectural Incompatibility

Spreadsheet applications such as Microsoft Excel are frequently employed as Gantt chart tools in project management contexts, despite persistent reports of operational failure in production environments. This paper provides a structural analysis of why this practice fails beyond mere implementation difficulty. We argue that the failure is architectural: Excel's computation engine operates as a directed acyclic graph (DAG), enforcing strict unidirectional causality from input to output. Gantt chart management, by contrast, requires bidirectional state synchronization, constraint satisfaction, and iterative rescheduling—capabilities fundamentally incompatible with a DAG-based model. Attempts to bridge this gap through Visual Basic for Applications (VBA) event-driven programming introduce circular trigger patterns that mirror Excel's circular reference prohibition at a higher abstraction layer. We further analyze the role of cognitive bias (availability heuristic, representation confusion) in sustaining the practice and situate the cultural persistence of Excel Gantt charts—particularly pronounced in Japanese organizational contexts—within the framework of interpretive flexibility in the social construction of technology. We conclude that the incompatibility is not incidental but constitutive: Gantt chart management requires a constraint satisfaction system, whereas Excel provides a functional composition engine. Recognizing this distinction offers a principled basis for tool selection in project management practice.