Policies are conjectures. They rest on theories about the causes of societal problems and further theories about how they may be resolved. Such conjectures are always fallible and even in rather modest reforms, the original hypotheses often fall short – vital preconditions are left unconsidered and unanticipated consequences arise. In complex policies, such as in national responses to the COVID-19 pandemic, the gap between policy expectations and public response is potentially vast. Before the arrival of the vaccination programme, UK virus management involved introducing hundreds of interventions in an unprecedented exercise in social control, known collectively and colloquially as “lockdown.” The chapter examines the fortunes of the underlying policy conjectures using a complex systems framework. It argues that the sheer complexity of this package of interventions generated scores of emergent and unanticipated effects, requiring revision after revision to lockdown policy. In modern, open, highly connected societies, the capacity for maintaining strict social control over a protracted period is severely limited. Lockdown has an in-built tendency to wax and wane in its effectiveness. Significant consequences follow for crisis management and for evidence-based policy.