It is most convenient to use the origin of the coordinates to examine the relationship between two points on the coordinates. Only by having the coordinates and the origin of the coordinates can we define the points on the coordinates and analyze the relationship between the points. Even if the points are real and the coordinates are imaginary, The position of the point is also relative to the coordinates.

For example: the crowd has left, middle and right. The left and right are not only relative to the right and left but also relative to the center. After that, if the left is the left and the right is the right, then the left and right need to be defined first. If there is no center, there is no such thing as left or right. On the contrary, the current left may become right if its definition changes, and right may also become left. This is the so-called relative. It can be seen that things are both connected and opposite.