Although academics are increasingly engaging with businesses, some fundamental aspects of this phenomenon (i.e., their motivations, decision-making approaches, and the interplay between the two) remain understudied. We therefore conducted a qualitative inductive study comprising 68 interviews with academics who had engaged in two forms of activities—knowledge transfer and co-creation. Whereas the entrepreneurship literature offers a resource-based argument, we made an original contribution to the literature by introducing an engagement-based argument in order to offer a more accurate prediction of the motivations and decision-making approaches of academics engaged in knowledge transfer and co-creation activities. We found that when the resource- and engagement-based arguments offer different predictions of the interplay between the motivations and decision-making approaches adopted, the cognitive proximity between academics and business researchers, which reflects whether the partners are from the same/different disciplines, resolves the puzzle. We captured these situational contingencies by developing six propositions that indicate how the engagement- and resource-based arguments jointly offer a more comprehensive explanation of the interplay. We discuss the implications of our findings with regard to how universities could offer customized training, rewards, and support structures based on the four types of interplay between the motivation and decision-making approaches.