What is the clincher for the entire selection of Tell Tale Heart?

The clincher of Edgar Allan Poe's "The Tell-Tale Heart" is the narrator's descent into madness, culminating in his confession of murder. Despite his insistence on sanity, the overwhelming guilt manifests as the imagined sound of the victim's heartbeat, driving him to reveal his crime. This climax underscores the themes of guilt and the psychological effects of conscience, highlighting how it can unravel even the most calculated plans. The story ultimately illustrates the inescapability of one's own guilt and the fragility of the human mind.