In the 2023 SWC Lecture, Stephen Reicher, Wardlaw Professor of Psychology at the University of St. Andrews, explains how the Covid-19 pandemic taught us the integral role of behavioural science (alongside other sciences) in responding to major societal challenges. He also describes how the pandemic showed us the costs of making erroneous assumptions about the drivers of action and the limitations of the perspectives currently dominant in Government behavioural science. Live illustration by Alex Cagan.