The inventors of the two-step-hypothesis, the Columbia researchers, touched upon a major problem in mass communication: The differentiation of the target groups in terms of individual receptiveness. But they did not answer any of our important questions. On the contrary. Biased by their research tradition they worked themselves into a blind allev. This fallacy influenced the development of the mass communication theory in a negative way. I have therefore described the main causes of that misadventure in an appendix to this paper.