Forces occur in opposites and equal pairs. This means that for every force exerted on an object, there is an equal and opposite force exerted by the object on another object. This concept is based on Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. In other words, when one object exerts a force on another object, the second object exerts an equal and opposite force on the first object. This principle is fundamental in understanding how forces interact and affect the motion of objects.