Inadequate nurse staffing in hospitals leads to increased morbidity and mortality. Two proposed explanations are that nurses provide surveillance and reassessment, which are particularly important for seriously ill patients, and that inadequate staffing leads to missed nursing care. This retrospective cohort study assessed the impact of a 2016 Massachusetts law that mandated minimum nursing ratios in intensive care units. Mortality and complication rates did not change after the law's passage, nor did they differ from states without staffing ratio mandates. Nurse staffing was not substantially higher in Massachusetts after the mandate when compared with other states. Two accompanying editorials highlight the challenges of measuring and promoting appropriate nursing care, which authors argue cannot be simply defined with a staffing ratio. A PSNet perspective and a WebM&M commentary further explore the safety risks of missed nursing care.