This case study provides an explanatory account on the underachievement of three gifted students studying physics in a Taiwanese university. The students' physics underachievement was diagnosed by Sato's student-problem analysis chart. These students were invited to complete a questionnaire and a follow-up interview in order to (1) understand the association between their academic performance, self-concepts, and support systems, and (2) elicit the pattern of their learning behaviors. Students reported that their self-worthiness was not undermined by their underachievement and they still believed in their own potentials. The study indicated that these students started to encounter academic problems during their senior high school years. The following learning habits resulted in their underachievement: (1) a lack of motivation and not applying self-actualization on subject matters, (2) focusing on memorizing and mastering skills and exercising counterproductive learning strategies, (3) a lack of genuine interest in the subject. This study also found that although these students had clear career goals and generally positive conceptualization of self, their professional development suffered from a lack of execution.