Magic is forgetting the world was ever other than as you willed it.
-- Morozko (Part One: 4. The Fate of All Witches)

Importance: This quote establishes the type of magic that is present in the novel. This power is not dependent on the type of person someone is or what magic they may have within them. Instead, it can only be used by those with the mental fortitude to imagine a life that is different from reality. Just as Vasya forgets that fire can burn her or believes that the bars of her cage can be bent, magic is limited to one’s imagination. However, the side effects of bending reality are harsh, and Vasya herself must battle madness for the entirety of the novel every time she uses her abilities.

Curse the silver-tongued priest,' Sasha thought. 'And curse Vasya too, wherever she is. For he could defend her good intentions and her good heart, but he could not...
-- Sasha (Part One: 8. Between the City and Evil.)