One such stress is magic, another is emotion. Normal animals do not have emotions, they have feelings. A dog can feel a great abiding, loyal, friendship with his human owner. A wolf can feel great affection for his mate. But true, deep, abiding love is a human emotion.
Mental anguish is a human emotion.
It is the gift and burden of intelligence. Humans have the capacity, by virtue of their minds, to experience a broader range of possibilities than any animal. There is something unique about the humans, elves, and other races which make them slightly different from the rest of nature. It is this ineffable quality which allows us to love, and to hate. A Farren has two parts of his being out of three which have no conception of what true love is, or hatred, or agony of the soul.