You Guys Are Ignoring The Suicide
If the entire film is Henry having a near-death experience, what's the point of the whole suicid angle? Why would someone have that kind of experience? Or, more appropriately, why would a writer want to put an audience through that experience.
The more obvious and less interesting explanation is that Sam was a witness o the crash, was traumatized by it, and then created a multipl-personality out of Henry. He'd been so moved by the crash that he found everything out that he could about him, hence why he knew what he did. Also, any scene between Henry and Sam never involves anyone else, except a blind man. And, because he's distraught and feels he must atone for not saving Henry, Sam returns to the scene of the accident where his imagined Henry threatens to commit suicide. If this imagined Henry commits suicide it will be the end of Sam. So, when Henry pulls the trigger in the end, that's Sam killing himself.
But this theory is somewhat shot out of the water by the way the blind man is later given sight and sees Henry and makes a distinction between Sam and Henry...it's just downright confusing...and if it is a near-death experience, while it's better than the standard split personality, it's slightly ludicrous because no one in that situation would look at Sam and then develope an entire plot in their mind where Sam has a girlfriend and then investigates Henry's life and speaks to a dead mother and a dead dog and such. It's just...hard to believe.
It's a shame because I really enjoyed the movie, it's very well made and very cool. But through the last forty minutes I was dissapointed because the clearest, simplest explanation is multiple-personality and that's overdone, but then in the end nothing is explained, which in a way I like, but at the same time I really want to understand the movie and feel like an idiot because I can't.