Having to change careers after losing a job can disrupt individuals' paths and aspirations, thus posing a threat to their ability to build sustainable careers. However, little is known about how these individuals navigate the career change and what enables or prevents them from regaining agency over their careers. Drawing on Zimmermann's (2024) agentic model of capabilities to aspire, we conducted qualitative longitudinal research to explore how workers who lost their jobs and had to change careers develop and pursue new aspirations. We carried out abductive temporal thematic analysis on four waves of semi-structured interviews, over four years, with six individuals who were changing careers following redundancy. We examined the participants' trajectories and the conversion factors that facilitate or hinder the realization of their career aspirations. Results show that several intricately linked conversion processes shaped the unfolding of the participants' aspirations. The case of Marie, a bookseller forced to change careers after losing her job in a saturated sector, is emblematic of these evolving dynamics. Four main processes characterized Marie's journey after her redundancy: desynchronization (having to postpone the realization of her life aspirations), fluctuation (coping with an unstable balance between relational support, material constraints, and identity transformation), polarization (positive conversion factors consolidating over time, but negative conversion factors becoming diffuse and unpredictable), and pervasiveness (feelings of uncertainty, marginalization, and stagnation spreading throughout her life). Overall, this study provides a balanced perspective on how agency and structure interact to shape career trajectories, thereby advancing the conceptualization of sustainable careers. In particular, we propose viewing sustainable career transitions as those that increase or preserve individuals' sense of control over their careers while nurturing their capability to aspire—i.e., their freedom and power to design desirable future goals.