How can you know when an object has an unbalanced force on it

If forces on an object are balanced, it stays in place. Like if two equally strong people push opposite sides of a box, the box will not move. If an object has unbalanced forces acting upon it, it will move the direction the greater force is directing its force. Like if a toddler and a bodybuilder pushed opposite sides if a box, the bodybuilder would move the box, and the toddler would be trampled.