Have you ever wondered, why is it that when you put one finger in front of you, you can see it clearly. But when you put the finger closer and closer till it stop right in front of your eye, you can only see something blocking your view. It no longer looks like a finger, it only looks like a blurry undefined thing.
Maybe in life, we should see things accordingly in the right length, which is different among people especially if they are short or near-sighted. When we see things too far, the eyes can't process it and when we see things too close to your eyes, the same thing happens, our eyes can't process it.