ever looked for jellyfish at the beach? they aren't exactly invisable, and yet ppl can't see them. they look at the water, thinking they are going to see something in it. some things in life you can't see directly, just evidence they are there. to find a jellyfish you look at the sand. you look for shadows, even the invisable cast shadows. find the shadow, the evidence of it's existance, though it may be small and faint, it's there.
that's what their existance amounts to............... shadows in the sand.