That isn't what I mean. That's what makes it possible, but as you've noted the possible is not precisely part of the equation.

[He takes a deep breath. Teaching magic was difficult enough, sometimes, but teaching it to someone that wasn't willing was more so. But the children in Corambis had bucked against his ideas too. He could deal with this]

Listen to me. Most often, spell-casting is not something that happens without a trigger. Incantations spoken, words written, gestures made, effects visualized. Anything can be the catalyst and it differs for every world. For me, it's a matter of intent and concentration but clearly you're doing something to set it off without the desire or effort.