Time, uncertainty, flexibility and resilience are the four sides of the same square around which this paper revolves. Hallmark of all complex systems is uncertainty, seen as the lack of full knowledge of current or future evolution of a system. There are various types and sources of uncertainty, but notably the incorrect knowledge of the environment in which a system operates determines the technological obsolescence and functionality of the system. Systems that have the longest life span are able to cope with the unpredictability of their contexts, while rigid and unchanging systems have a shorter lifespan. Uncertainty, traditionally seen as a negative aspect of a system, must therefore be regarded as an opportunity, an incentive to design flexible systems able to absorb changes in the environment in which they operate, in order to create added value for users. The development of “advanced” systems able to prevent that uncertainty generates diseases, commonly referred to as “risks”. This is not new; the selection process of species of Darwin, or the reflections on the life of capital goods of Terborgh, have shown that there are living organisms, human artifacts or resilient complex systems that are better equipped to adapt to changing environments, compared to the rigid systems incapable of reacting to change. In other words, flexibility reduces the exposure of a project uncertainty, provides a solution to mitigate market risks, and also mitigates risks associated with technological obsolescence. Flexibility makes the system resilient, able to absorb shocks and/or disturbances without undergoing major alterations in its functional organization, structure, or identity characteristics. In this paper flexibility is seen as a fundamental property for designing a generally complex system.