What is the implication of a finding of unreasonableness for the recovery of a plaintiff?

36. Turning now to the implication of a finding of unreasonableness for the plaintiff's recovery, it is clear that the so‑called "duty to mitigate" derives from the general proposition that a plaintiff cannot recover from the defendant damages which he himself could have avoided by the taking of reasonable steps. As Pearson L.J. pointed out in Darbishire v. Warran, supra, it is not a "duty" in the strict sense. A breach of it is not actionable. Quoting from his reasons at p. 1075: ...it is important to appreciate the true nature of the so‑called "duty to mitigate the loss" or "duty to minimize the damage." The plaintiff is not under any contractual obligation to adopt the cheaper method: if he wishes to adopt the more expensive method, he is at liberty to do so and by doing so he commits no wrong against the defendant or anyone else. The true meaning is that the plaintiff is not entitled to charge the defendant by way of damages with any greater sum than that which he reasonably needs to expend for the purpose of making good the loss. In short, he is fully entitled to be as extravagant as he pleases but not at the expense of the defendant.