This chapter, “When to Walk Away,” examines the underexplored decision to terminate aerospace and space exploration projects. It challenges the romanticised norm of limitless perseverance, advocating for explicit, data-driven exit criteria amid technical, financial, and regulatory uncertainty. Drawing on industry cases, including technological dead ends, loss of funding, regulatory shifts, and strategic misalignment, it outlines practical frameworks for early detection of project inviability. The chapter analyses cognitive and organisational biases, such as sunk-cost fallacy, corporate ego, and groupthink, that impede rational judgement. It offers tools for transparent evaluations, independent reviews, and milestone-gated funding to enforce disciplined decision-making. Termination is reframed as strategic prudence rather than failure, highlighting opportunity costs and the benefits of reallocating resources to higher-potential initiatives. Integrating insights from engineering management, finance, and governance, the chapter provides actionable guidance for entrepreneurs, executives, and investors to institutionalise robust exit processes. By fostering a culture of timely withdrawal, it seeks to strengthen resilience, sustainability, and long-term value creation in the high-risk domain of space ventures.