The backbone of Geotechnical Engineering does not concern the development of more or less sophisticated tools and theories. It remains in a previous step. When facing a real problem it is necessary to isolate its fundamental aspects and to achieve a correct conceptual representation of its nature. This phase requires abstract thinking, which is certainly assisted by a proper understanding of paradigms and theories of Soil and Rock Mechanics. The process of abstract thinking with the aim of identifying the key issues usually renounces to complexity and secondary details. To be successful, concepts should be simple and rooted on well established mechanical and physical knowledge. Only when the relevant mechanisms or phenomena which define the problem are well understood, additional sophistication may be added for a more accurate analysis or interpretation. This book remains in this first "simple" stage. The correct identification of the essential traits of a geotechnical situation relies heavily also on accumulated experience and on educated intuition. But, how to educate intuition and how to transfer practical experience? Geotechnical failures, specially the catastrophic ones, are an excellent experience and a source of inspiration to improve our current understanding of phenomena and our procedures and tools for analysis and prediction. This unconventional manner to learn Geomechanics is the essence of this book which teaches how to build the necessary models to understand failures. Balance and equilibrium equations are formulated at different scales which are selected having in mind the abstract representation of the key concepts of each case.