Magical Balance

Significant sources of magical power require a repayment in exchange for providing their power. In essence, it is the conservation of mass/energy, but in the form of magic. When you draw from a significant source, such as the sun, the moon, or the stars, you must use a replenishing ritual to make up for the energy you've taken. This ritual doesn't create magic but is a spell to assist that magical source in recovering its losses quickly.

In the event that magic is taken without replenishment, that source of magic will turn against that user. This is a little explored area, though some believe it proves magical sources have a consciousness of some form. The source will slowly refuse to provide further power to a magical user after repeat infractions. Ultimately it will begin to seek out and take the magic user as compensation for its losses. In the case of the Earth, plants may rise up to capture the magic user. Celestial sources like the moon could burn the magic user from the world or send magical creatures for them. A manifestation, an avatar of those bodies, could seek out the magic user personally.