What is the difference between a mutual mistake and a unilateral mistake?

As set out in Wilde v. Wilde, 2000 CanLII 22544 (ONSC) (“Wilde”) at paras. 24-25, a mutual mistake is to be assessed on objective grounds looking at whether a reasonable person in the circumstances would decide that an agreement had been reached; while a unilateral mistake, there is a subjective element to the standard, by which the party claiming to have been mistaken may show the effect of that mistake in her or his own mind. As Linhares de Sousa J. observed in Wilde (at para. 24), “if either [mutual or unilateral mistake] are found on the facts then the parties cannot be said to have been of the same mind on the Agreement.”