"Lesson" is a Middle English word that has been defined as "a passage from sacred writings read in a service of worship" as well as "something learned by study or experience". The term is quite appropriate in assessment of what has been learned from randomised trials in adult low-grade gliomas, since the treatment of these tumours has traditionally been guided as much by belief as by fact. Therefore, when assessing these trials we can apply the principles of hermeneutics. Thus, the first meaning of "lesson" given here can be described as literal, whereas the second may be seen as figurative. Since hermeneutics may also refer to an in-depth analysis of a particular text, the investigators will present their interpretation of data from randomised trials. The goal is to show that the lessons learned are not necessarily literal or dogmatic but can be much more allegorical in nature.