Influence Effects usually erode when the spell’s Duration ends. Long-term conditioning, however, can convince the target that the spell truly is his reality. (See the Social Conditioning

That’s especially true if the Effect fits his existing beliefs or personality. Influence that suits the subject’s usual inclinations is far more effective – and lasts much longer – than influence that runs against the subject’s grain. Mind-controlling a pacifist to kill, for instance, would go against her beliefs (and would thus wear off quickly), while casting the same Effect upon an angry sociopath would simply influence her to do things she might do anyway (and so might not wear off at all). A smart mage, then, picks targets who would be inclined to go along with his plans for them whether he was using magick to influence them or not.