In this presentation, Jean Pariés shows that optimization strategies – based on the anticipation and standardization of “one best way” responses, also have a perverse effect: by reducing the diversity and variability of systems, they reduce what is called their resilience: the ability to handle the unexpected. He also suggest ways to preserve this capacity, because it is more and more necessary in a world paradoxically at once more and more regulated and unpredictable. Indeed, day after day, the news from the world confirms the growth of change, turbulence and complexity, the reign of surprise, and the need for adaptability and resilience.