What is the test for retraining a plaintiff in a motor vehicle accident?

39 As I put it in Palmer v. Goodall at page 59: But with comparatively young plaintiffs ─ and I do not propose to define "comparatively young" save to say that 31 is well within the description ─ the jury must be told that it is for the plaintiff to show the extent to which his ability to earn a living as it existed before the injury has been impaired. In many cases, a plaintiff may show that in order to earn as good a living as before i.e. to restore his earning capacity he requires retraining. The cost of retraining, if it is a reasonable proposition, is a proper element of compensation. Because it is impairment that is being redressed, even a plaintiff who is apparently going to be able to earn as much as he could have earned if not injured or who, with retraining, on the balance of probabilities will be able to do so, is entitled to some compensation for the impairment. He is entitled to it because for the rest of his life some occupations will be closed to him and it is impossible to say that over his working life the impairment will not harm his income earning ability.