Widespread enthusiasm for implementing rapid response systems (RRS) has been tempered in part by mixed impact on clinical outcomes. One argument for why RRS have not proven uniformly effective has been that they are underutilized in patients who might have benefited. Supporting that argument, this study found that 42% of adult patients with physiological instability failed to have an RRS activated despite meeting explicit written criteria. Furthermore, in these cases nearly 70% of providers recognized that the criteria were met and 76% were concerned about their patient, yet they did not activate the RRS. Structured interviews with staff members pointed to sociocultural reasons for failing to activate, and improved triggers and activation criteria were felt unlikely to have an impact. The authors conclude that local unwritten rules and culture may drive adherence to such written policies in more meaningful ways than the policies themselves.