In this paper, I propose an accurate description of the cognitive process involved in the one-sidedness fallacy, a widespread type of fallacy. I describe first several characterizations of the one-sidedness fallacy, that are either inductive or deductive, or occurring at a meta-philosophical level. I recall, second, the framework of the cognitive distortions described in Franceschi (2007). I give then a definition of the one-sidedness fallacy, by describing it as a general cognitive distortion: the disqualification of one pole. I show finally (...) how the one-sidedness fallacy distinguishes itself from the confirmation bias. (shrink)