Blind spots are human nature. They occur in regions in our eyes where our retina meets out optic nerve. A blind spot is a part of the visual field we can't see because of an absence of rods and cones. Our brain fills in the gaps created by our blind sports, so that is why we don't notice them daily. Blind spots really are the most extraordinary illusions.
Below is a picture that shows you your blind spot. Cover up your left eye and focus on the cross hairs while looking at the black dot with your peripheral vision. Slowly move your eye closer to the screen. At a point, the black dot will disappear; thus, your blind spot.