Dijkstra went on a trip to California, visiting universities and research centers. While doing so, he got annoyed by the many researchers who viewed the difficulties underlying multi-person software projects as "communication problems" and who, therefore, advocated new specification languages.
In Dijkstra's words:
I fear that "the communication problem" is a misleading euphenism, the acceptance of which explains parts of the almost morbid preoccupation with "specification languages" and the like. [EWD774]
Instead, the difficulties, according to Dijkstra, are due to lack of explicit rigor. Lack of rigor is already present in single-person projects, but it becomes even more apparent when multiple people need to work together on the same project.