What is the test for putting a plaintiff in a better position than their original position?

The defendants need not put the plaintiff in a position better than her original one and should not compensate the plaintiff for any damages she would have suffered anyway: Blackwater v. Plint, 2005 SCC 58, at para. 78. In determining the plaintiff’s original position, it may be necessary to reflect any debilitating effects of a pre-existing condition, or a measurable risk that such a condition would have detrimentally affected the plaintiff in the future regardless of the defendant’s negligence. This is the crumbling skull rule and, where applicable, it results in the damages award being reduced to reflect risks inherent in the plaintiff’s pre-accident condition: Athey, at para. 35.