Here's why:

* Motion is relative: An object can be in motion relative to one object, but stationary relative to another. For example, a person sitting on a train is moving relative to the ground, but stationary relative to the train.

* Reference point provides a frame of reference: To understand motion, we need a point of comparison. The reference point establishes a frame of reference that tells us whether something is moving or not, and how it's moving.

Let me know if you'd like more examples or have other questions about motion!