A truck operated by N. Fiorito Co. (Fiorito) (defendant) made a left turn in violation of the rules of the road and collided with a car driven by Derheim (plaintiff). Derheim was not wearing a seat belt and suffered severe injuries as a result. Derheim sued Fiorito for negligence. At trial, Fiorito sought to introduce evidence that Derheim was not wearing his seat belt to establish Derheim’s contributory negligence. Fiorito sought a reduction in damages based on the doctrine of “avoidable consequences.” Fiorito argued that had Derheim been wearing his seat belt, his injuries would have been less serious. The trial court refused to admit this evidence, and the jury awarded a verdict for Derheim. Fiorito appealed directly to the Washington Supreme Court.