You should watch this video:
In sort, everybody has a blind spot and most people do not even know they have it. You can make it visible with a little trick. Still the brain always "unsees" it. The same is true for the blood vessels directly over your retina. They cast a permanent shadow over your retina and you can make them visible (again, with a little trick). Still the brain will always ignore the actual information from the eyes and use filters/memory the create the better picture. So the brain completely ignores information form your eyes 24/7. It is so efficient en effective in doing so that almost nobody knows you can see the shadow of the blood vessels directly over your retina. Think about that....