This study examines two students’ reasoning processes when solving a Calculus problem, focusingon their discourse characteristics and factors influencing narrative endorsement. Using videorecordings of paired discussions, the results show rituals, social acceptance, ambiguity,inconsistency, and the impact of mathematical representations as characteristics of the narratives.The results also indicate that rituals and ambiguities are key factors in determining whether thenarrative becomes endorsed. Additionally, ambiguity provides opportunities for the two students tothink critically and creatively, which can support their reasoning process.