What must a defendant do to discharge the duty of care owed to a plaintiff?

What a defendant must do to discharge the duty of care owed to a plaintiff is determined by the conduct expected of the law's invention, the reasonable person, as adjusted to the circumstances of each case. Since, as we have observed, negligence involves exposing another to an unreasonable risk of harm, the risk to which a defendant is expected to respond must be real and consideration must be given to what a defendant should do, or not do, to guard against the objectively determined risk. The precautions that must be taken to guard against a particular risk will vary directly with the magnitude of the risk. We would add that the trier of fact should not assess a defendant’s conduct with the benefit of hindsight. See Lapointe v. Hôpital Le Gardeur, 1992 CanLII 119 (SCC), [1992] 1 S.C.R. 351.