The purpose of this paper is to contribute to the advancement of knowledge on how to manage the perceived complexity by project participants. For this, we carried out a case study approach and we chose an R&D project carried out by an SME, which was partly co-financed by a public entity. We use a qualitative approach for our research. In addition, we conducted semi-structured interviews, at the beginning, and at the end, of the co-financed part of the project, using the Complexity Assessment Tool (CAT) as a scheme. The results showed the usefulness of the CAT to guide the responses to the perceived complexity and the use of social capital and human capital as a source that is used by the participants in the project to develop the responses. Our work extends knowledge about the importance of developing responses to complexity and the sources from which they arise.