When an author uses first person point of view to narrate the story, his or her aim is to draw the reader into the story, so that they can feel as if they were an actual part of the story itself. This is what happens in The Tell-Tale Heart as well - when we read about the paranoia that the protagonist is feeling after murdering his landlord, we can almost feel that ourselves, experience the same things he is, and fear for him as much as he fears for himself.