Characterized by specific and rigid boundaries of institutional practices and expectations in the academy, student writing is a synergistic literacy practice where students are required to construct generically diverse texts by yoking concepts with appropriate linguistic resources. This empirical study involving 196 first-year ESL students at a university in Sri Lanka explores why conceptual incongruities occur in argumentative essays constructed by them, and how they defend their arguments. We analyzed all their timed essays and noticed that 72 out of them contained conceptual incongruities. By "conceptual incongruities, we refer to instances where students" conceptualization process is not aligned or coherent with the essay topic. For our analysis of student texts, we have introduced two social cognitive perspectives: untutored competencies and tutored competencies. The former includes inherited, social, and ideological identities emerging from societal epistemologies whereas disciplinarity and interdisciplinarity constitute the latter. This empirical research demonstrates how students' conceptualization process is mediated by a labyrinthine repertoire of knowledge premised in students' untutored competencies and tutored competencies, signaling deviations from their essay topic.