He seeks out the sender of the note, a man called Elijah, played by Samuel L. Jackson. Elijah is unfortunate enough to have a disease that causes his bones to break easily. He had broken limbs when he was born, he couldn't play with other kids because he was so fragile; in school he was nicknamed "Mr. Glass". Because of his condition, Elijah spent all his time reading comic books, and he became obsessed with the supernatural powers of comic book heroes, so much so that he now runs a comic book shop that carries priceless limited editions.
The mysterious stranger starts showing up and asking questions, showing a great interest in David's life and his failing marriage. He suggests that David has special powers, that he has been sent to help humankind like some kind of comic book hero. This, not surprisingly leads David to believe that Elijah is crazy, and perhaps even dangerous, but when Elijah almost gets killed proving that David does have special powers, David starts to take notice. David's son actually becomes so obsessed with the idea of his father being a superman, that in one harrowing scene the confused little kid tries to shoot his dad to see if the bullets will bounce off.
Like The 6th Sense, Unbreakable unfolds slowly, taking its time to examine David's marriage, his relationship with his son, and his inner confusion. I personally prefer this kind of film to the kind with constant fast action which seem to be aimed at those with the attention span of a five-year old. Unbreakable is intelligent and thought-provoking; I left the cinema with the feeling that perhaps we all have latent powers which are simply waiting to be discovered...