Blind spot.

We all think we see everything. But in fact, our eyes are blind spots that do not perceive light, and this area is called "blind spot." Blind spots are found in every human being in different places of the eye. But there is one available in 95% of the people.
That's exactly what "blind spot" we suggest you find yourself in.

Look at the picture below. Close the right eye and the left to see the cross on the right (the one in the circle). And, slowly, it approaches the screen, then keep away. Left cross that you see the edge of the eye, will disappear at some point. That's just such a phenomenon is called "blind spot."