User blog comment:LaviBookman/Magic Discussion/@comment-1399043-20120620072510/@comment-973828-20120620165728

Most fantasy magics work that way anyways: in Dungeons & Dragons (which many believe modern fantasy magics take root from), a wizard uses his own body energy to cast spells, so if he runs out of energy, he can die from exhaustion. However, magic in D&D is also very complex, with different types of magic such as arcane, ritual, divine, psionic (mental magic), primal (nature magic), and dweomer (aura magic). It's not very clear if a user's own energy applies to all forms of magic in D&D.