A psychoanalytic treatment can fail for many reasons, and the impasse is only one of them; but it is so singular that it merits preferential attention. Stealthy and silent, the difficulty of detecting and resolving it is intrinsic in its nature, as is studying it and reflecting on it. It is perhaps the worst risk in our hazardous occupation and the most certain threat to our instrument of work. Just one of these cases is sufficient to shake our scientific ideology, because impasse is not simply an internal difficulty of the theory both a real anomaly, which brings into question the psychoanalytic paradigm and threatens with a crisis. And in general it does not present itself to the newly trained analyst but to one who already has sufficient experience to remove more visible obstacles.