What the main idea in the story Poe's final days?

The main idea of "The Tell-Tale Heart" by Edgar Allan Poe was about a murderer who is insistent that his is not insane for killing an old man who had a weird-looking eye. This indicates that the murderer, the narrator of the story, is constantly paranoid about the old man, and apparently murder solves his problem. However, he may not be so lucky by the end of the story.