Y.
We take in everything we see. We just can't process it all at once. However, we can mentally re-create our experience.
THis is why hypnosis works so well with helping victims and witnesses of crimes re-create their visual impressions for the sake of prosecution.
However, we cannot react to what we don't see. That's why blind shots, undulating fairways, and other architectural tricks baffle and fascinate us.
It's also why a blind shot is only blind once. After the trick has been revealed to us, we're not easily fooled again. If we are repeatedly fooled, we've run into some excellent GCA, or we're really stupid, or just not very observant..
It onlt takes once, if we're paying attention.