In this article we use the recent Covid-19 crisis to investigate what motivates individuals in their decisions to deal with two externalities, namely disease transmission, in particular social distancing, and the willingness to undertake green expenditure. As motivators we look at economic egoism (homo oeconomicus), altruism, moral norms, social norms and regulation. We develop a survey to measure these motivators, the two externalities, and also standard socio-economic control variables. Our results, based on 1,356 responses, suggest that individuals missperceive both their own motivators for dealing with the externalities as well as the drivers of other people’s decision. In addition, they misevaluate the importance of social motivators for their own decisions. We discuss the repercussions of these two results for environmental policy, in particular cooperation and coordination, as well the evaluation of welfare changes.