Here's why:

* Newton's Third Law: For every action, there is an equal and opposite reaction.

* Rocket Propulsion: A rocket engine burns fuel, creating hot gas that expands rapidly. The expanding gas is expelled out of the rocket's nozzle (the action). This expulsion of gas creates a force in the opposite direction, pushing the rocket upwards (the reaction).

Essentially, the rocket pushes the gas out, and the gas pushes the rocket back. This is the principle of action-reaction that allows the rocket to overcome gravity and launch into space.