ABSTRACT A discussion during the INCOSE International Symposium 2025 revealed a persistent misunderstanding regarding functional allocation and encapsulation in hierarchical system models. In particular, this was illustrated by the question of whether thrust is produced by an airplane or by its engine. While thrust itself is not the focus of this paper, the question serves as a concrete and instructive example of a deeper conceptual issue: the conflation of system‐level behavior with subsystem‐level allocation, and the improper interpretation of encapsulation across hierarchical levels. This paper addresses the thrust attribution question by first examining it through constructs from general systems theory, emphasizing system boundaries, black‐box behavior, and encapsulation. The argument is then formalized using Wymore's mathematical modeling framework for open systems. The paper concludes by discussing implications for systems engineering practice and analyzing why such misunderstanding may persist in mature engineering domains despite well‐established theoretical foundations.