Why do some policies succeed in bringing about widespread social change, but others founder?

In his annual RSA Chief Executive’s Lecture, Matthew Taylor examines the relationship between policy-making and social change. What distinguishes successful policy changes - for example, the smoking ban - from other ideas that seemed to have everything in their favour at the outset, and yet ultimately failed to deliver?

Is there a key to truly impactful policy creation and implementation? Or, to meet the scale and urgency of the challenges we’re currently facing, do we need to start thinking differently about how change happens - looking beyond policy to nothing less than a new paradigm for society and social progress?