The octroying of forms in a medium can only ever be selective. It exploits certain possibilities and, by favoring them, eclipses others. All Learning in school therefore presupposes corresponding *prohibitions of learning*; and in view of the openness of a medium, naturally much more learning must be prohibited than released by teaching.
~
Luhmann, Niklas (1991). Das Kind als Medium der Erziehung. doi 
, p. 32.