The assessment and implementation of development projects has been disconnected from relevant concepts in social psychology, especially those relating to understanding the interac-tions between projects and local communities. This disconnection has given rise to the prevalence of several fallacies about human behaviour amongst project staff, decision makers and environmental and social impact assessment practitioners. The playing-out of these fallacies influences the implementation of projects and reduces the likelihood of gaining a social licence to operate. Because these fallacies lead to distorted perceptions about com-munities, the existence of these fallacies is deleterious to desirable social relations with communities, good impact assessment practice, and to effective project decision-making. We describe eight of these fallacies: subjectivity; naiveté; unpredictability; irrationality; greediness; self-serving; aggressiveness; and rigidity. We discuss these fallacies by drawing on the social psychology constructs of attitudes, risk perception, social identity, and social justice. We conclude by considering how these fallacies can be addressed in practice and how develop-ment projects and impact assessment can be improved.