Two persistent trends in the development of modern technologies have been the decreasing importance of physical prowess and the increasing importance of intellectual skills. Complex systems must be designed, managed, operated thoughtfully. The present talk describes some central results in the scientific study of intellectual processes and points to their implication for reliability engineering. It does so on a general level, relying on representative studies and suggestive applications: This overview is intended in part to set the stage for the following talks which demonstrate the sort of detailed work needed to produce recommendations for particular problems, and to evaluate their effectiveness.