Reporting on a growing trend toward large and complex systems, this article explores the role of human error in system safety redesign. With the evolution of systems described, arguments are made for challenges in linking errors as a specific behavior rather than an effect of changing work environments. Discussion includes the causal analysis of accidents, human error and behavior, human and system adaptation, and control of safety in complex systems. Based on presented information, the author calls for new system design approaches with greater emphasis on addressing structural deficiencies rather than human reliability.