One has various reasons for not seeing what's right in front of one's nose. Visual noise is one of them: there is so much to see around us, that we can't possibly notice everything. Our brain-power is simply not up to decoding everything. Those of us with dyslexia have the problem in spades. Something in our brains routinely switches things around, causes our attention to jump around, and does various other dastardly deed which suggest a death-wish.

I once saw a presentation years ago, where the speaker displayed a visual demonstration of how much brain-work is done processing what we see. A picture was shown, and then changed back and forth to change some feature. The feature was blatant -- nothing subtle about it. Yet the first time he did it, I never saw it. Meanwhile everyone around me was exclaiming over the picture.

He repeated the demonstration, and I finally saw it: someone was wearing jeans that shifted between ordinary color and bright kilt-colored. Yes it was blatant, but I only saw it a minute or so after it appeared. Yes, I was one of those exclaiming.