This paper argues that it would not be possible to design technological systems to eliminate all human errors during operation because people are involved in: specifying, designing, implementing, installing, commissioning and maintaining systems as well as operating them. The paper illustrates this with examples of incidents caused by human error and concludes that, even if systems can operate without human intervention, there is still the possibility of human error at other phases of the lifecycle. Thus to improve process safety it will be necessary to focus on behaviour and methods of working during all phases of the lifecycle so as to remove or reduce opportunities for human error.