In this article it is argued that people behave unhealthily or change their unhealthy behaviour, not primarily out of the wish to be healthy, but to feel good and positive about themselves. First it is explained that people continue to perform their health-related behaviours because they feel the need to be self-consistent. Second, it is demonstrated that people are motivated to reduce the self-threat which occurs when they are confronted with the negative health consequences of their own behaviour. People engage in self-maintenance strategies, which may reduce self-threat without the need to change risk behaviour. Next to the wish to feel good about the self and to be self-consistent over time, people are motivated to develop and enhance the self. Mechanisms by which people seek self-improvement are feedback from observing others and through enactive learning. In addition, people adapt their health-related behaviour in response to contextual stimuli in order to preserve or enhance their self. In conclusion, it is demonstrated that most instances of irrationality are related to silent preverbal motives to enhance or preserve a positive self, whether this has healthy or unhealthy consequences. The implications for health promotion interventions are discussed. (Netherlands Journal of Psychology, 62, 42-50.)