The paper offers a new interpretation of one of the most famous ambiguous doppelganger pieces in world literature, E.A. Poe’s “William Wilson” (1839) the inconsistencies of which are notorious. Those are generally attributed to Poe’s “unreliable narrator.” Poe’s tale is set aside in the article with another, equally well-known doppelganger text, to “The Jolly Corner” (1901) by Henry James. The comparative study aims at highlighting the difference in the two writers’ approaches to building up ambiguity and, consequently, the difference in the reader’s reception of these texts. The numerous explanations of “William Wilson,” previously suggested in Poe’s scholarship, - as a moralizing parable, a study in psychopathology, a story of twins, a dream narrative, etc. - tend to ignore the inconsistences. Paradoxically, the tale presents a special challenge to Poe scholars rather than to the ‘naïve’ readership. Knowing his aesthetic theory of the “unity of effect,” one cannot help but suspect that all the paradoxes of “William Wilson,” its carefully placed logical traps were predetermined. The paper employs the instruments of Gestalt-psychology and methods of cognitive literary criticism to provide a new reading of Poe's novella as a case-study of cognitive dissonance. In such an interpretation, the inconsistencies of “William Wilson” turn out to be paradoxically effective.