Although the use of theories and evidence is often stressed in the development of health promotion interventions, this does not guarantee the success of an intervention. Thus, we need to reflect on intervention development processes that use different types of theories and evidence. In this paper, we provide a reflective discussion on how we identified evidence-based behavior change techniques and counseling themes for a health promotion intervention. In addition, we discuss the challenges that we encountered and what we learned during the process: a) a lack of previous research and meta-analyses, b) inconsistencies in evidence, c) integrating evidence and theories that have different starting points, and d) collaborating with researchers who represent different evidence and theories. During the process, we benefitted from having the clear goal of conducting evidence- and theory-based work. We solved the challenges by, for example, utilizing different types of evidence and being reflective about the reasons behind any inconsistencies in the evidence. In retrospect, we would have benefitted from closer collaboration between the teams that worked separately with different evidence. These kinds of reflective descriptions of development processes and the challenges encountered during them may help other researchers and professionals avoid encountering the same challenges.