The management of uncertainty during a project's implementation is not well understood. In general, uncertainties are treated similar to project risks by practitioners and by scholars as negative events threatening a project's implementation. Following the arguments of economists, uncertainties are a necessary condition for the existence of opportunities. This research aims to identify specific classes of opportunities and specific contextual situations under which they occur during the implementation of projects. An exploratory case study of 20 projects was conducted. Different categories of opportunities and uncertainties were identified. All identified opportunities were connected with at least one situation of uncertainty but not every situation of uncertainty relates to opportunities. The cases unveiled that risks are misperceived as uncertainties and some situations of project improvements were misperceived as opportunities. Our study sheds light on the limitations of classic project management and suggests that future project management education needs to include a deeper exposure to business context to better equip project managers for the challenge and opportunity posed by uncertainty during project implementation.