Why do action and reaction forces not cancel each other on the same object?

Action and reaction forces do not cancel each other out because they act on different bodies, not on the same object.1

According to Newton’s third law of motion, when two bodies interact, they exert forces upon each other that are equal in magnitude and opposite in direction. Because each force in this pair is applied to a distinct object, they cannot combine to produce a net force on either individual body.21

It is important to distinguish these from balanced forces. For example, when an object rests on a table, the downward force of gravity and the upward force exerted by the table act on the same object, resulting in equilibrium. These two forces are balanced, but they are not an action-reaction pair. The true action-reaction pair involves the object pushing down on the table and the table pushing up on the object; since these forces act on two different bodies, they do not cancel each other out.1