The book explores the concept of self-organized criticality, a theory in the field of complex systems, which explains how complex natural phenomena such as earthquakes, biological evolution, and economic fluctuations inherently organize themselves into a critical state, poised between order and chaos. The author uses a wide range of examples and simple models to illustrate how this state is reached spontaneously and without specific design, and how it can lead to sudden, unpredictable events. This theory challenges traditional scientific views on the nature of complexity and provides a new perspective on the dynamics of the natural world.