the X that can be Y is not the true X Yet another instance of hackerdom's peculiar attraction to mystical references - a common humorous way of making exclusive statements about a class of things.  The template is from the "Tao te Ching": "The Tao which can be spoken of is not the true Tao."  The implication is often that the X is a mystery accessible only to the enlightened.  See the trampoline entry for an example, and compare has the X nature. 
[Jargon File]