What is the most obvious case in which a court may find a breach of the standard of care in the absence of expert evidence?

The “most obvious of cases” in which a court may find a breach of the standard of care in the absence of expert evidence about that standard are those in which accepted practice is “fraught with obvious risk” such that a breach of the standard of care may be found on the basis of common sense: ter Neuzen v. Korn, 1995 CanLII 72 (SCC), [1995] 3 S.C.R. 674, at paras. 38-41 and 51-52 [ter Neuzen]. The example cited in ter Neuzen of such an exceptional case involved a physician who left a sponge in a patient during surgery, resulting in the patient’s suffocation.

Even where a plaintiff has established breach of the standard of care, she must also prove that the breach caused injury to the plaintiff. The test for causation is the “but for” test; that is, the plaintiff must show that but for the defendant’s breach of duty the injury would not have occurred: Clements v. Clements, 2012 SCC 32 at paras. 8-10; Tripp at paras. 38-40.