Technically speaking, this double role creates a number of difficulties for the actor. He has to perform with a partner who is not there. He has to interact with someone who is only wind, but the ghost’s response determines a vast range of things. This answer, which will be shot immediately after or the next day, and again the person to whom it is addressed is absent. Audiences and even people in the trade can hardly imagine the degree of concentration, the continuous replacement of I with you, that was needed to create the effect obtained by the director. Happy is the actor whose performance rests on an idea. This time round that was the case for me. I discovered once again that film is the ultimate art for expressing my feelings.
Conrad Veidt, “B.Z. Mittag”, March 19, 1926

The film tries to analyze characters using just one actor to represent fundamentally different human beings. We cannot deny that Conrad Veidt did not manage to make these two characters convincing. The camera did not always succeed in making us believe that they were two different individuals. In the scene where the two brothers confront each other, it often seems that they do not look at each other, that they move around one another without seeing each other, which weakens the overall effect. (…) We are less than satisfied because we read the novel. And Kellermann did not conceal his hope that they would make a serious film out of it that would stress his ideas and thus become a social and economic warning. If Kellermann saw the film, it is hardly likely that he would think it corresponds with viewpoint of the novel. The details that remain are insignificant to the author, merely external aspects; in other words, everything that was cinema in the old meaning of the word. It is all the more a shame because for once a social film could have shown active men belonging to different social strata.
Anonymous, Die Brüder Schellenberg, “Filmschau”, March 1926