Where, as here, there are multiple tortfeasors, the defendants are not excused from liability because other causal factors for which they are not responsible also contributed to produce the harm. As long as a defendant is part of the cause of an injury, the defendant is liable, even though his or her act alone was not enough to create the injury: Athey v. Leonati, 1996 CanLII 183 (SCC),  3 S.C.R. 458 at paras. 17-20.
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