People share and encounter a range of posts on social media that depict different career experiences, such as one's successes or failures. In a continually shifting world of work, observing others' job experiences can be useful for navigating one's own career journey. The present study applies the possible selves theory to understand how viewing people's career experiences on social media might affect viewers' career-related expectations, hopes, and fears. From semi-structured interviews with 19 social media users with different career experiences, this study found that social media posts may facilitate functions of possible selves by 1) increasing people's awareness of new and diverse career paths and 2) motivating people in planning and preparing for a desired possible self. Across these functions, we found that videos were particularly beneficial for uncovering and learning about life in a career and that observing others' career experiences online often evoked social comparison. Through an affordances lens, findings also indicate that social media affordances of visibility and persistence were particularly relevant in developing and assessing career-related possible selves and sometimes strategically managed through leveraging platform algorithms. This paper brings forth empirical contributions to the possible selves theory in the digital age and highlights the significance of social media mechanisms for possible selves. This paper also provides design implications for social media platforms and recommendations for potential career counseling and mentoring strategies that may be useful for individuals navigating and exploring career possibilities.