In general, in our ordinary life, we manage to make the difference between "strange" behavior and error or extravagant beliefs. The question is here to know how we do so, and against what background. There are also specialized contexts for evaluating whether certain types of behavior or discourse are normal or abnormal: courts of law and psychiatric hospitals are two examples. In these contexts, judgments are formed against a background of technical or scientific knowledge, but they also result from epistemic means of evaluation that are similar to habitual ones. The paper seeks to highlight this similarity with respect to recognizing mental disturbance. Starting from Wittgenstein's On Certainty, it attempts at extending it by drawing on notions of reciprocal perspectives and of judgments of incongruity. It documents its investigation by analyzing sequences from Malek Bensmail's documentary, Aliénations, which examines the treatment of mental suffering in contemporary Algeria.