In any city, in any country, go to any mental institution or halfway house you can get yourself to. When you reach the front desk, ask with no hesitation to visit someone who calls himself "The Holder of Me". The worker will just stare blankly at you, as if puzzled. Ask him a second time. Again, the worker will just stare at you, without moving. Now just wait. For your health's sake, don't ask a third time.
The worker will finally, slowly stand up and will guide you through a door that opens on a narrow straight pathway brightly lit from above, too long to see the ending. On the walls of the pathway there are uncountable paintings: their expressions are of utter and complete pain, mouths screaming in despair and foreboding unfathomable horrors. Your gaze seems attracted to their faces, but you must stay strong and divert your eyes: do not gaze any of the paintings for more than 2 seconds or the subsequent unbearable scream of madness from it and from the others would lead you to rip off your ears first and your brain thereafter.
The first painting on your left depicts the worker that led you to this room. Walking down the corridor you'll notice that the paintings depict every person you met in your entire life, complete strangers first and then, as you advance through the corridor, casual acquaintances, friends, intimates, relatives and finally, at the end of the pathway, your parents. When you reach these last two paintings, turn back: if you still see the corridor then you were not ready, and pray that starvation and dehydration kill you before insanity ensues, because you'll never leave the corridor again.
If your spirit is indeed ready enough, you should instead see a wall with an empty frame on it, surrounding a sheet of complete darkness. Walk through the frame and you'll be in a dark room: you can feel that the room is very large, but do not move and don't say anything. What lurks in this room doesn't like to be disturbed too early. When your eyes have adapted from the light to the darkness, you'll notice that there is a figure in the distance. He stands motionless. Slowly advance towards it, it will do the same: eventually you'll notice that it mirrors every movement you do. Once you notice this, stand still, close your eyes and say "I'm here". Open your eyes: the figure will be closer, and you'll be able to see that it resembles you, although you still won't be able to discern his face. Don't walk towards it, and don't move. Close again your eyes and say "I'm here to know": opening your eyes will reveal that the figure is two meters away from you. You can see that it looks like you, except that his eye sockets are empty and bleeding, as if something tore its eyeballs away. Again, don't go towards it and don't move. Close the eyes for a third time, turn around and say "I'm here to know myself", then slowly walk backwards: if your back hits a solid surface then you're free to scream until the pain kills you, your eyes exploding with a loud and bloody "pop" and your spine torn away from your back.
If you don't hit anything where the figure should have been, then continue to walk until an unbearable pain from feet to knees, as if someone was crushing your legs, will cause you to fall face on the floor. Don't open your eyes and don't even try to stand up: in the darkness you'll be able to hear a distant laughter, as if someone or something was mocking you. While still on the floor ask the question "Who am I?": the laughter will then come closer, increase in tone and pitch and become hysterical, and as your ears are pierced by it and it completely surrounds you, threatening to lead you mad, every moment of your life will pop in front of your closed eyes in a swirling pattern of colors, sounds, smells and tastes, sharp and vibrant, beautiful yet gruesome and gloomy, exposing all your secrets and all your hidden shames, leading you to understand the Nothingness of your pathetic existence in front of the greatness of Everything as if your soul was literally ripped from your heart and leaving you on the brisk of insanity.
When the images cease, the pain at the legs will disappear and you'll be able to stand again, if you're still sane: in front of you, on the ground, there will be a cracked mirror. Every time you look through it, you hear the faintest echo of a laughter coming from it.
The mirror is Object 1111 of 2538. Now you have the knowledge of who You are: can you bear it?
Credited to Garnet