How does the expression you protest too much apply to the narrator's comments about his sanity?

The expression "you protest too much" suggests that excessive denial can indicate a hidden truth. In the context of the narrator's comments about his sanity, his fervent insistence on being sane raises suspicion rather than providing reassurance. His repeated declarations serve to highlight his instability, suggesting that his protests may be a cover for his actual descent into madness. Ultimately, this irony deepens the tension between his self-perception and the reality of his condition.