Should fear guide our actions and governments’ political decisions? A leitmotiv of common sense is that emotions are tricky, they blur our rational capacity of estimating utilities in order to plan action and thus they should be banned from any account of our rational expectations. In this paper I argue that an “heuristic of fear” is the appropriate attitude to adopt in order to cope with extreme risks. I thus defend the Precautionary Principle against the criticism put forward by Cass (...) Sunstein and other authors on the basis of a new analysis of extreme risks or “ruin-problems”. (shrink)