Purpose: This study attempts to clarify the difficulties faced by healthcare professionals in South Korea in making and implementing Life-Sustaining Treatment (LST) decisions for vulnerable patients who lack legally competent proxy decision-makers. Materials and Methods: First, a keyword analysis was performed on the official responses of the National Health Agency of Korea to 750 questions from healthcare workers. Second, a survey probing the difficulties that healthcare professionals face in making LST decisions was administered to the ethics committee members of 246 medical institutions. Results: From the keyword analysis, 139 keywords were categorized into ten subcategories. The survey had a 32.5% response rate, and of the respondents, 41.98% faced difficulties in making decisions for unrepresented patients because of the absence of family members or due to inadequate evidence. Among these patients, 82.35% did not have decision-making ability at the time of need and 85.29% had no family members to consult with. Conclusion: Four categories of “unbefriended” patients were identified in this study. Additionally, in uncovering evidence on how LST decisions are implemented and creating a category of “unbe-friended patients,” this study underscores the need to expand the scope of legal proxies under the LST Decisions Act.