Balance recognizes that many good things in life are good only in moderation. There really can be too much of something wonderful. Most virtues, taken to excess become vices. When an interest, affection, or endeavor becomes utterly consuming, it doesn't allow room for other kinds of goodness.
Implicit in the concept of balance is the notion that two very different things are true at once, and both must be heeded. Simply illustrated, we need to work, and we need to play. We need to give out, and we need to replenish. We need to go wild, and we need to be calm. Each of us is prone to fall out of balance in our own way. To maintain balance requires that we value balance. It also requires intention, mindfulness, and self-discipline.