Reusing software have been a constant challenge through the 50 years of the software engineering. In the last decades, the variability has been considered a fundamental aspect to manage the systemic reuse of software, and to propose approaches such as system families, software product lines, software factories, feature-based development and generative programming have been proposed based on the analysis of variability. In this talk, David will talk and reflect on the challenges that exist in these subjects that many authors consider the foundation for developing software products in the next decades.