Many software projects fail: they take more time than they were intended to, go over their budgets, and do not achieve the intended functionalities. Software project failures occur, in part, because software project managers (SPMs) often fail to manage project risks. Researchers have developed many risk management prescriptions to guide SPMs, including risk checklists, frameworks, practices, and risk response strategies. However, research has shown that SPMs do not use these prescriptions widely. This study addresses the research question: why do many SPMs not fully engage in formal risk management? The question will be answered using a case study approach. The findings will extend our understanding of software project risk management by demonstrating why SPMs sometimes act so differently from formal prescriptions.