Brehmer begins from the individual's role in safety of complex production systems. In reviewing various theories about unsafe acts, "human error", accident proneness, and human characteristics that have sought to establish causality between individuals and system safety, he contends that this path has borne little fruit. Although many accidents have been caused by operator errors, little can be done to improve safety by changing decision making at this level. As far as shop-floor attitudes and motivation are concerned, group norms and habits are probably more important than those of individuals. To achieve systematic improvements one has to move up the organisation and study changes in decision making there.