This is a perfect example of hubris, a concept from ancient Greece. It is a character trait of extremely confident people - overconfident people in fact - that often leads to their downfall, as is the case in The Tell-Tale Heart. A direct quote from the story for why the narrator places his chair over the burial place of the old man is, "while I myself, in the wild audacity of my perfect triumph, placed my own seat upon the very spot beneath which reposed the corpse of the victim." This is a perfect example of hubris: in his overconfidence in this situation, he is basically taunting the police - he is practically telling them where the body is, so they must be stupid if they could not figure it out, which meant that he was smarter than them. Unfortunately, this overconfidence leads to his own overwhelming guilt, which leads him to confessing his crime. Had he just remained humble and not taunted the police, he could possibly have gotten away with it.