Quickness is like looking out the window of a speeding train. You don’t get to see the surroundings closest to you. They are nothing but blurs. Your view lacks details and in-depth description. If you focus on a distant object though, you can easily see the entire picture. Like Calvino discusses, quickness seeks to eliminate the unnecessary and focus on the crucial parts of the story.
In the E-Lit example, stories are told at their minimum. One could easily create a novel out of one story alone, but instead it is contracted into a single page. Details would only blur the purpose, therefore they are told as if they were far from the train window. We can see them clearly that way.