AbstractBertolt Brecht once closed a text with the words “We are disappointed to see the curtain close and all questions are left unanswered” [1]. In this book, it has become clear that uncertainty is immanent in the product life cycle of technical systems in mechanical engineering from (B) production, (C) usage, (D) reuse to (E) sourcing. The latter is the starting phase of the following sequence B, C, D, E. Uncertainty has been relevant since the beginning of the industrialisation, cf. Theodor Fontane’s ballad ‘The Tay Bridge’ quoted in Chap. 10.1007/978-3-030-78354-9_1 and this will continue to be so. Hence, we will never see “the curtain close”, but a perpetual contribution of engineering science, applied mathematics, law and further branches of science to master uncertainty in mechanical engineering.