The genius of Terry Pratchett.
In this quotation from Unseen Academicals – about sports, ugh – my favourite Discworld character, Havelock Vetinari, explains his first encounter with evil and what that meant to him in terms of moral engagement.
The Patrician took a sip of his beer. “I have told this to few people, gentlemen, and I suspect I never will again, but one day when I was a young boy on holiday in Uberwald I was walking along the bank of a stream when I saw a mother otter with her cubs. A very endearing sight, I’m sure you will agree, and even as I watched, the mother otter dived into the water and came up with a plump salmon, which she subdued and dragged on to a half-submerged log. As she ate it, while of course it was still alive, the body split and I remember to this day the sweet pinkness of its roes as they spilled out, much to the delight of the baby otters who scrambled over themselves to feed on the delicacy. One of nature’s wonders, gentlemen: mother and children dining upon mother and children. And that’s when I first learned about evil. It is built into the very nature of the universe. Every world spins in pain. If there is any kind of supreme being, I told myself, it is up to all of us to become his moral superior.”
The two wizards exchanged a glance. Vetinari was staring into the depths of his beer mug and they were glad that they did not know what he saw in there.