"That the desk constitutes an obstacle to my physical movement is due to the particular distinctions my sensory system enables me to make and to the particular way in which I have come to coordinate them. Indeed, if I now could walk through the desk, it would no longer fit the abstraction I have made in prior experience. This, I think, is simple enough. What is not so simple is the realization that the fact that I am able to make the particular distinctions and coordinations and establish their permanence in my experiential world, does not tell me anything other than the fact that it is one of the things my experiential reality allows me to do." (von Glasersfeld 1991, "An Exposition of Radical Constructivism: Why Some Like it Radical").