" YOU SEE THEM SOMETIMES.
They're just out of the corner of your eye, when you're not expecting them, and sometimes if you close your eyes very, very tightly, and open them quickly, there will be a quick flash of them behind your eyelids before they dissipate.
They are the echoes of deja vu, they are the regrets that are fleeting, they are that which you didn't know you missed...
They are everywhere and nowhere. "
― Peter David , The Quiet Place (Star Trek: New Frontier, #7)