Poe had an acute understanding of what goes on beyond the "double locked" doors of the human mind, both in terms of what we carefully shut away from others and what we shut off from ourselves.
Two examples of carefully locking away the murderous and irrational impulses of the human psyche occur in "The Cask of Amontillado" and "The Tell-tale Heart." In both stories, the protagonist carefully hides his desire to kill from his intended victim and the rest of the world. Montresor makes it very clear that Fortunato has no idea of the rage burning in his breast over the "thousand insults" he feels he has suffered over the years from this "friend." In fact, nobody suspects that he has chained Fortunato in his catacombs to die until he makes what seems a deathbed confession to his priest fifty years later. Likewise, the protagonist of "The Tell-tale Heart" keeps his loathing from the old man he has taken an irrational dislike to because of his "evil" eye—and later convincingly persuades the police that he is innocent. It is only his own guilt that leads him to confess, not any suspicion from the police. A sub-theme of both stories, therefore, is how possible it is for a person who seems perfectly normal and well balanced to be hiding dark, evil secrets.
The knowledge we hide from ourselves is not so double locked away, but Poe nevertheless explores ways we try to delude ourselves. In "The Tell-tale Heart," the narrator tries to find rational explanations for his behavior so that he can deny—which he forcefully does—that he is insane. In "The Masque of the Red Death," the revelers in the palace try to lock away the knowledge that they are no more immune from the plague than everyone else, although the hourly loud chiming of the ebony clock is a reminder that they, too, will one day die.