What is the test for determining whether a plaintiff’s life would have gone without the tortious injury?

In Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458, 140 D.L.R. (4th) 235, at 27-28: “Hypothetical events (such as how the plaintiff’s life would have proceeded without the tortious injury) or future events need not be proven on a balance of probabilities. Instead, they are simply given weight according to their relative likelihood. For example, if there is a 30 per cent change that the plaintiff’s injuries will worsen, then the damage award may be increased to 30 per cent of the anticipated extra damages to reflect that risk. A future or hypothetical possibility will be taken into consideration as long as it is a real and substantial possibility and not mere speculation.”