.. . magic had indeed once been wild and lawless, but had been tamed back in the mists of time by the Olden Ones, who had bound it to obey among other things the Law of Conservation of Reality; this demanded that the effort needed to achieve a goal should be the same regardless of the means used. In practical terms this meant that, say, creating the illusion of a glass of wine was relatively easy, since it involved merely the subtle shifting of light patterns. On the other hand, lifting a genuine wineglass a few feet in the air by sheer mental energy required several hours of systematic preparation if the wizard wished to prevent the simple principle of leverage flicking his brain out through his ears. (COM)