The balance within a living organism is called homeostasis. It is best understood if we think about maintaining hydration.
The body, specifically cells within the body, have an optimum water content and regulates the sensation of thirst and the production of urine to ensure that the balance between water in and water out is maintained. In situations where we can not take in water (stuck in the middle of the Sahara Desert for example) the body will begin moving molecules in and out of cells to maintain the required amount of water within each cell. It does this to achieve balance (aka homeostasis) within the cell to allow it to function.
Companion animals and humans strive for this in physical movement as well. They must balance forces to maintain physical fitness and health. To achieve this they must have the nutrients necessary and understand the movements to balance their body effectively.