Supply-side economics, popularly known as ‘trickle-down’ economics, has been the most dominant approach to economic policy in North America (and some other countries) since the 1980s. Despite all economic evidence to the contrary, it is a policy that is still pursued today, to some extent or other, by both conservative and centrist parties in liberal democracies. The primary real-world consequence of these policies is a drastic increase in the economic differences between the rich and poor. The record is not good. Why is the policy so popular?