Shared understanding is essential for efficient communication in software development and evolution projects when the risk of unsatisfactory outcome and rework of project results shall be low. Today, however, shared understanding is used mostly in an unreflected, intuitive way. This is particularly true for implicit shared understanding. In this paper, we investigate the role, value and usage of shared understanding in Software Engineering. We contribute a reflected analysis of the problem, in particular of how to rely on implicit shared understanding. We discuss enablers and obstacles, compile existing practices for dealing with shared understanding, and present a roadmap for improving knowledge and practice in this area.