One of the early discoveries made by social psychologists was that people can influence our behaviour just by being there when we are doing something. Sometimes, other people's presence can mean that we do things better, a phenomenon known as social facilitation. Coaction effects happen when the person feels personally responsible for the end results. The report of the murder prompted a series of psychological investigations into the behaviour of bystanders. Social impact theory has been described as a clear example of reductionism in psychology. According to this theory, the origins of social behaviour are in the way that the person combines and unconsciously processes the social forces impinging on them. One of the aspects of human social interaction which makes phenomena like group polarisation and groupthink so likely to happen is the way that we much prefer to agree with one another, rather than challenge and confront.