If the defendant proves that the harm would have occurred anyway, irrespective of the defendant s act or omission, then the negligence action will fail for lack of causation. Imagine that a patient is suffering from ovarian cancer. The physician admits the patient to the hospital. The element of duty is now satisfied because once the physician undertook care for the patient the physician had a clear duty to exercise reasonable care toward the patient. Ovarian cancer often develops rapidly, and can be hard to diagnose until it has progressed to an advanced stage.
Lets say the physician failed to make a proper diagnosis of the patient s condition.
In our hypothetical, the patient dies in the hospital. The patient s death would satisfy the element of damages. Now the court would look to the element of causation. If a medical expert was unable to say with reasonable certainty that a correct diagnosis would have saved the patient s life the negligence action will fail and the physician will not be found liable. Despite the fact that the physician negligently misdiagnosed the patient s condition, the misdiagnosis did not cause the patient s death.