Here's why:

* It acts on every object with mass: This means that regardless of the size, shape, or composition of an object, if it has mass, it will be affected by gravity.

* Every object with mass exerts gravity: This means that not only does the Earth pull you towards it, but you also pull on the Earth, just with a much smaller force.

Essentially, gravity is a fundamental force that governs the interactions between all objects with mass in the universe. It's not just a force pulling us down to Earth, but a universal force that holds galaxies together and influences the evolution of stars and planets.