[Celestia responds to the attack on her horn quite forcibly, hurling out a blast disproportionate to the attack. It cracks out into the sky like a column, and with her attention distracted thusly, the shadow makes it beneath her without her notice.]

If I cast a spell on you to make you feel love or fear or happiness -- if I used magic to change your behavior and your emotions, even if you asked me to, I would be taking your will way. Why is this different?