Here we see an example of Posner's use of economic analysis to help shape common law.  Economists view people, and the institutions whose fortunes they guide, as rational wealth maximizers, each acting in its own economic self interest. Accordingly, as Posner suggests, it would be unreasonable to imply in an insurance contract a duty to cooperate with an insured to avoid offending a customer because the premiums charged by the insurance company do not reflect the risk of collusive (wealth maximizing) behavior by the insured and the customer.