The aim of this study is to propose a set of necessary and sufficient conditions for robustness. To this end, a set of definitions and a postulate about unpredictable variability and uncertainty are presented, proving that minimising the number and strength of dependences is a sufficient and necessary condition for robustness and value. They also proved that Axiomatic Design's Independence and Information Axioms can be derived as theorems in the frame of this work. Several academic and industrial examples are presented to illustrate the results. Finally, the internal and external consistency of the theory, enunciated as the Principle of Weaker Dependences, is discussed as well as its generalisation in terms of the Principle of Reflexive Practice.