This is a crucial point of Newton's Third Law of Motion.

Here's why:

* Action: One object exerts a force (the action force) on another object.

* Reaction: The second object simultaneously exerts an equal and opposite force (the reaction force) back on the first object.

Examples:

* You pushing a wall: You exert a force on the wall (action), and the wall exerts an equal and opposite force back on you (reaction).

* A book resting on a table: The book exerts a force on the table (action), and the table exerts an equal and opposite force on the book (reaction).

* A rocket launching: The rocket expels hot gas downwards (action), and the gas pushes back on the rocket upwards (reaction).

It's important to remember that action-reaction pairs never act on the same object. They always act on two different objects.