This study aimed to identify which topics are challenging for Korean teachers to teach, the reasons behind these challenges, and their preferred teaching approaches. The investigation focused on the concept of difficult knowledge, which encompasses the emotional and affective aspects encountered by learners when tackling challenging subjects, as well as the practical knowledge possessed by teachers when instructing such topics. In-depth interviews were conducted with elementary school teachers majoring in social studies in Seoul and Gwangju, and a narrative case study was employed to qualitatively analyze the findings. The study revealed that the knowledge regarded as difficult for teachers to teach in South Korea is often intertwined with political ideology, including topics like the Gwangju Uprising, the history of sexual violence, and subjects related to sexuality, such as LGBTQ issues. Three primary characteristics of teachers who tackle these challenging topics were identified. Firstly, some teachers recognize the importance of these subjects but refrain from teaching them due to concerns about their students’ cognitive and emotional readiness. The second group of teachers chooses to address the “difficulty” by solely relying on textbook content. Last, there are teachers who actively seek to learn and expand their knowledge to effectively teach difficult topics. These findings shed light on the social context surrounding difficult knowledge, particularly in South Korea. The unique dynamics of South Korea’s relationship with North Korea make history topics linked to political ideology particularly challenging. Additionally, the culture of familism prevalent in South Korea significantly influences the education system. The common difficulty faced by teachers when teaching subjects related to sexuality and death is rooted in their own emotional experiences with difficult knowledge. These findings have implications for understanding the social and local contexts, considering appropriate student readiness levels, and enhancing teacher education for teaching difficult knowledge in the future.