The world's gone crazy. We are overwhelmed by a continuous outpouring of fake news and conspiracy theories, by ordinary hatred on social networks, by the radicalization of points of view, in everyday life, in the family circle, on the roads, at work... Generally speaking, the tone is rising, in a mixture of feverishness, versatility, and without much respect for each other. The situation is such that the defence of rationality in public debate is often inaudible, even unthinkable. This book will therefore appear as a provocation. It proposes to understand our contemporary impotence in the face of what many call post truth society, by inviting us to go behind the scenes of this collective madness.