Here's why:

* Gravity is attractive: It pulls objects towards each other.

* Center of mass: This is the point where the mass of an object is concentrated.

* Motion away: If an object tries to move further away from the center of mass, gravity pulls it back.

Examples:

* Jumping: When you jump, gravity pulls you back down to the Earth.

* Throwing a ball: When you throw a ball upwards, gravity slows it down and eventually pulls it back to the ground.

* Orbiting: Objects in orbit are constantly falling towards the Earth due to gravity, but their sideways motion prevents them from crashing.

In essence, gravity is constantly trying to pull things together. It opposes any motion that would increase the distance between objects.