Abstract
Mainstream economics assumes that people act rationally – i.e., to promote their interests. Behavioural economics (BE) observes that in fact, people act by rules of thumb, which sometimes lead to irrational behaviour. These positions are perfectly consistent: people act by rules, which usually work well but may work poorly in contrived scenarios. The reason is that like physical features, behavioural rules have evolved; and evolution works in naturally occurring – not contrived – scenarios.
