Film doesn't make sense

How could Crowe possibly not realize he's dead until the very end? The few coincidences in the movie that fool the viewer into thinking he's alive (he happens to be sitting facing a living person, tricking the reader into thinking they can see and hear each other; he calls to his wife to answer the doorbell, and we can't see her lack of reaction because she is upstairs) would not have kept Crowe himself fooled over all the months following the home invasion/shooting, because there would have been hundreds and thousands of instances where he tried to interact with a living person. He would have quickly picked up on the fact that they cannot see or hear him.