First Law of Magic
The power of a spell is in direct proportion to the training, magical aptitude, and passion for its success of the caster.
While the magical fields of Fillimet are available to all creatures, using magical abilities typically requires training. Some species or individuals have more innate aptitude for using spells, while others need to use a Focus to use any magical abilities. Above all else, for a spell or magical ability to work the caster needs to truly wish for success. If this intention wavers, even for a moment, unintended consequences may occur. Additionally, many believe the effects of Vitriol Magic stem from this magical law. Much as a spell's success hinges on the intentions of its caster, the risk of malamancy affecting that spell hinges upon these same desires.