Knowledge demands sacrifice.
— Ancient Craving, Magic: The Gathering
"With the thirty-seven keys of Tzeentch, we open the way for our brothers! With the thousand whispers of Slaanesh, we call to them! With the twelve plagues of Nurgle, we fell their enemies! And with the mighty axe of Khorne, we cut open the world for them!"
"In magic, there is neither good nor evil. It is merely a science. The science of causing change to occur by means of one's will. The sinister reputation attached to it is entirely groundless and is based on superstition, rather than objective observation. The power of the will is something that people do not understand, attributing to it mysterious qualities that it does not posses. Being simply the power of 'mind over matter'. Or, in the greater number of cases, the power of mind over mind. As your mind now is succumbing to mine..."
—Mocata, The Devil Rides Out
Pain erupted in my left palm. The power was cold-and not mountain-breeze cold, either. It was slimy and nauseating, like something that had come slinking out from the depths of some enormous subterranean sea. In that instant of contact, my head exploded with terror. This power, this black magic, was wrong. Fundamentally, nightmarishly, intensely wrong.
—Harry Dresden, The Dresden Files
Black magick isn't a matter of tools or rituals - many primal styles use rites that make "civilized" people blanch. Black magick comes from motivation, from spite, hatred, rage, lust. It twists, burns, compels, commands. It's a mystickal shotgun aimed at the heads of your enemies, a knife in the heart of everyone you despise. More often than not, a maleficent magician strikes bargains with Infernal entities - the devils and demons her parents warned her about - and appeasing them with sacrifices, blasphemies, vandalism and terrorism. The ultimate power, however, comes from the hatred within the mage, not from demonic pacts. Although some lesser powers flow from demonic hands, the true black magician holds the keys to her own damnation... gladly.
—Mage: The Ascension - The Orphan's Survival Guide