When, for example, you lose the use of a limb on your body, suddenly we would understand the value of that limb, how crucial it is for our convenience and use in life.
Like that, when we lose the peace in our mind, when we become stressed, anxious, angry, and so on, it would make us suffer so much. We would understand just how important it is to have peace in the mind.
So for this meditation is taught to rediscover that peace. We can be in control again of this precious mind.