It takes two points to define a line or the equation passing through both points.
There are an infinite number of lines passing through a single point.
Imagine you were standing on the point on a large sheet of graph paper.
Look straight ahead of you. That's your line of sight. What do you see? You can see all around you because there's nothing particular to look at.
But then your friend appears and you look at him or her. You now have something to look at, and you and your friend represent two points defining a line of sight. You look at each other, so there's your line.