In this study we perform extended Lessons Learned interviews concerning collaboration in multidisciplinary engineering projects at DLR, the German Aerospace Center. Interviews are held with all available members out of several project teams. The success of a project is evaluated against a) standard Lessons Learned scales (as used in Project Management, PM) and b) the perceived satisfaction of the interviewees. Furthermore, we inquire about the nature of collaboration and individual experiences. From the interviews we could identify the influence of four main factors: i) organizational structure; ii) organizational practice; iii) leadership and iv) continuity. The above factors cannot be captured with standard PM methods. These rather need to be “discovered anew” by project managers. The goal of our investigation is to let the practice of good “real live” project management flow into future projects and into education.