Do this sum once and it is hard to forget. You blink about fifteen times a minute, and each blink closes your eyes for a tenth of a second or a little more. Across a waking day that is around half an hour of darkness, cut into some fourteen thousand pieces, and you notice none of them, because the brain dims vision for each blink and stitches the picture together across the gap. Over a long life it comes to something like a year spent awake with your eyes shut, paid in instalments of a tenth of a second, and the film never once skipped.