A counterweight is crucial for magicians, needed in case an element threatens to overwhelm the magic user and draw him/her in. The mage would reach for the opposite element if they overextended themselves or are about to be drawn into the element. The opposing elements can also be used in battle, supposedly making them more effective against each other.
The concept and use of counterweight is included as the fifth principle in the "Five Principles of Magic": "All elements have a counterweight. Fire is the counterweight of water. Air is the counterweight of earth. The counterweight of chaos is the soul." Specifically, the counterweight of the void is the soul, and the counterweight of chaos magic is human life.