Balance is indeed the key tenet of magic and the Old Religion: in order for something to be taken, something must be given. This is very clear in the rituals related to the power over life and death (Le Morte d'Arthur) or the blood sacrifice (The Darkest Hour), where a life is required. Magic, however, can be performed in other ways, when the conjurer is linked to the power of the Sidhe (Sidhe magic) or trolls (Troll magic). But the Old Religion still remains the source of every power.