The greatest film noirs show you that the world is not as it appears and as we wish it to be, peaceful, comforting, safe. These movies portray people whose lives changed in an instant, by accident, by sudden decision. Their world then becomes the stuff of nightmares.
Depressing? Yes, but some emerge this way: "I think maybe I'm stronger and braver. I know I am. Because I know that everything we have is balanced on such a delicate web of incidence and coincidence." Roger Ebert says, "Because no society could have created a world so filled with doom, fate, fear and betrayal, unless it were essentially naive and optimistic."