In this paper, I try to sketch in general lines the idea of complementarity, which was first suggested by Niels Bohr as an answer to the conceptual problems of quantum mechanics, but later extended by him to other domains, both within science and outside it. In these applications, the idea of complementarity allows for the acceptance of different sets of beliefs and principles, which contradict each other but have all their value. In particular, it may help to ease the conflict between the scientific approach and human aspirations.