Error occurrence cannot be fully eliminated. A strict differentiation between errors and their consequences is used to (a) discuss error prevention and error management, and (b) to show how organisations can promote an error mastery culture that combines the best of both. This article uses two 1996 Everest expeditions as an illustration of what can go wrong in complex high-risk systems. The point of this article, however, is not restricted to high-risk industries. A mastery error culture aims at control of negative error consequences - most relevant in high-risk industries - but also fosters positive error consequences needed for adaptation and innovation. The article discusses both general and recent empirical literature on safety, quality and error handling.