This is a fundamental concept in physics known as Newton's First Law of Motion, also called the Law of Inertia.

Here's a breakdown:

* Inertia: The tendency of an object to resist changes in its motion. This means an object at rest will stay at rest, and an object in motion will stay in motion at a constant speed and direction unless acted upon by an unbalanced force.

* Unbalanced Force: When multiple forces act on an object, and the forces do not cancel each other out, resulting in a net force. This net force causes a change in the object's motion.

So, in simpler terms, an object will keep doing what it's doing (whether it's standing still or moving) unless a force pushes or pulls it in a different direction.