Mental habits could be considered a major determinant not only of physical health behaviors and status but also of mental health. However, there has been limited research on the concept of mental habits in Korea and internationally. As homeless people experience mental health issues more frequently than the general population, early detection and management could be crucial for improving their mental health. Therefore, this study aims to conduct a phenomenological study to discover common experiences of the homeless, focusing on the formation process of mental habits. Through the analysis of in-depth interviews with 12 homeless people, 21 themes, 11 theme clusters, and 6 categories were derived. The results suggested that the mental habits of the homeless were formed through experiences including social disconnection, addiction, unethical behavior, economic difficulties, social exclusion, chronic problematic environments, and intrinsic motivations for life. From childhood to the current homeless status, various experiences have led to complicated interactions affecting the interviewees in multiple ways: a single event could lead to multiple mental habits, or a combination of experiences could develop a single mental habit. Therefore, policies for homeless people should not simply aim to provide shelter but should also aim to end homelessness through supports for sustainable living. This should be built on an understanding of their experiences including life before homelessness, the process of becoming homeless, and their experiences as homeless individuals. Based on this, the researchers' policy recommendations are as follows: First, programs for the homeless should proactively aim to eliminate discrimination. Second, interventions for mental habits should incorporate specific and non-specific interventions. Lastly, interventions for the mental health of homeless people should focus on creating intrinsic motivations.