But this principle does make sense, in a strange "what is my brain doing" kind of way. A little bit of "whoa man, brains are insane" in there too. We've all seen examples of this principle, but we just may not have know what it was. For example, when you think you see a face in the dents of a carton of chocolate milk, or in the folds of a hanging pair of pants. While unintentional, these are both examples of the principle of closure.
Tom Friedman's hanging sculpture Open Black Box is another example of closure.
By using the angles of the corners to show the limitations of the 'box' Friedman creates a cube. The points coming off each piece direct your eye to the one parallel to it. He has eight different parts to the sculpture, but because of the gestalt principles we see it as one object.