After the meeting between Aglaya and Nastassya Filippovna, Myshkin begins to lose the last remnants of mental stability, which vanish entirely after Nastassya Filippovna's murder. Mirroring the decline in the prince's sanity, the narrator gradually loses omniscience throughout the novel. In the end, the narrator resorts to rumors and gossip in constructing the novel's events and cannot tell with any degree of certainty whether the events of the wedding actually occurred in the way he is about to tell. Much like Myshkin, who becomes more and more of an "idiot" as the novel progresses, the narrator too approaches idiocy in his inability to retell the novel's events with any certainty or interpret them with any credible explanation.

The Idiot ends having gone full circle geographically. Myshkin takes a train from Switzerland to St. Petersburg, follows Nastassya Filippovna to other cities, goes to Pavlovsk, returns to St. Petersburg, and finally is sent back to the clinic in Switzerland. The prince arrives in St. Petersburg like a messiah sent to help many of the main characters of the novel; however, he fails to save them from destruction and then returns to the clinic in a state of complete mental degradation. It may be extreme, however, to characterize his trip as a complete failure. Certainly, at the end of the novel, Nastassya Filippovna and General Ivolgin are dead, while the lives of Rogozhin and Aglaya are virtually ruined. Nonetheless, Myshkin has had an indelible effect upon the people he has met, particularly younger characters like Kolya and Vera Lebedev. Perhaps it is Dostoevsky's hope that Myshkin will also have an effect on us as readers. For now, however, the author suggests that society is not ready for a man of such profound goodness as the prince.