As is commonly known, the blind spot is what we call the small area on the retina where the optic nerve leaves the eye and which is insensitive to light. Paradoxically , it is the structure of the perceptional apparatus that prevents us from seeing perfectly. Moreover, it is due to this that we are able to see at all; this defect is essential. With this in mind, perhaps the expression does not seem blasphemous after all which says that everybody has his/her blind spot.