This training is based on the discussion method used in medieval universities, the disputatio. Originally, this method was used as an examination (in fact, certain modern exams at universities are remnants of it) in which the student had to demonstrate that he could explain all the aspects of a particular issue and give a fair estimate of both sides to it, leading to a well argumented conclusion.
In the modern version, the Magister method is done with a group. The participants still have to demonstrate insight into both sides of the issue (typically taken from the actuality of their work situations) and arrive at a fair conclusion. The result is that they learn to listen to “the other side” and find some consensus with it; a consensus which is not more nor less than is required for a decision on the issue at hand.