The German energy transition towards more sustainable forms of energy production has been characterized as a large-scale or real-world experiment. Whereas experiments are open-ended processes set up explicitly to allow (or even generate) surprises, by contrast sustainability implies the pursuit of clearly defined, normative ends. Whereas much of the literature on system transformation builds on the concept of innovation, our hypothesis is that focusing on the “natural” flipside of innovation—called here “exnovation,” i.e., departing from unsustainable pathways—should also be seen as a valuable conceptual strategy for coping with the tension between the unavoidable indeterminacy resulting from unknown risks and the necessary amendment and redefinition of goals and rules. In this paper the German energy transition (Energiewende) is used to exemplify the recursive processes of experimentation that make it possible to accommodate surprise, and, thus, to conceptualize the unavoidable tension between innovation and the maintenance of older, unsustainable structures.