Vertigo

     "The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents.  We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far."
     -H.P. Lovecraft, The Call of Cthulhu
   
     Look up, what do you see?  You might see a roof over your head.  The one over mine is white, textured. Behind the paint and texture is sheetrock, wood, insulation.  Roofing, shingles.  Beyond that is the sky.  And beyond the sky is infinity.
     But nothing goes on forever, not really.  So past the sky isn't really infinity.  It's merely massive, larger than we can comprehend, and so we call it 'infinity' and shove it into a drawer and stop thinking about it, because the human mind isn't capable of maintaining perception on that scale.  Lovecraft understood this, that maybe the most terrifying thing in the world is the simple comprehension of the absolute powerlessness of the human race.  Now, it may not seem that bad.  Everyone has looked into the sky and realized we are nothing more than a speck of dust on a speck of dust floating in the largest room in existence.
     What's scary is when someone accidentally inhales that speck of dust.  When objects on our scale meet objects on a scale beyond reckoning, and we get to see firsthand, to truly experience the powerlessness of humanity.  It's like vertigo.  Hanging from a cliff and looking down and seeing all that distance stretching out below you, beckoning.  The sudden irrational but irrefutable feeling that nothing is stable, the ground, gravity, your arms, all of it could betray you at any moment.  And if there's enough empty space below you, you'll go mad from it.  Most people don't see the empty space, though.  They see the clouds, and the texture of the cliff below them.  Some of them don't even see past their own feet.  Oh, sure, they know there's a fall below them.  They just don't understand exactly what that means until they open their eyes wide enough to see it.  And then their palms get sweaty, their heart starts beating fast, and they wonder how it's suddenly so terrifying hanging there, when a moment ago they were doing chin-ups and humming showtunes.
     So don't look down.  There's a point at which it just becomes too much, a point where understanding brings nothing but pain and madness.  You can pretend, sure.  Read, watch movies, write, imagine, there's no harm in that, because all you're doing is speculating at what's below you.  Chatting with the person hanging next to you, estimating the exact length you would fall if you were to let go.  Watch Cthulhu on a screen, but if you see him in real life, I have one word for you:
     Run.