What you see is not what others see. We inhabit parallel worlds of perception, bounded by our interests and experience. What is obvious to some is invisible to others. I might find myself standing, transfixed, by the roadside, watching a sparrowhawk hunting among the bushes, astonished that other people could ignore it. But they might just as well be wondering how I could have failed to notice the new V6 Pentastar Sahara that just drove past.