Our small self, the body-mind, is always filled with countless desires ... the desire to be somewhere else, be getting somewhere, achieving some prize, some distant goal. Our body-mind is always judging this or that as somehow inadequate to what the body-mind wants, its likes and dislikes, needs, regrets and dreams.
Thus, when there is sat an instant of Zazen as
wholeness in just sitting, the only place to be and act to do in that instant, in all of reality, to fulfill life as life ... the Buddha and all the Ancestors just sitting in that instant of sitting, no other thing to attain or which ever can be attained ... no other place to go or in need of going ... all holes filled, whether full or empty or in between ... all lack and excess resolved in that one sitting, with not one thing to add or take away ... judgments dropped away, "likes and dislikes" put aside ... nothing missing from Zazen (
even when we might feel that "something is missing", for one can be fully content with the feeling of lack!) ... the sitting of Zazen and all life experienced as complete and whole as just the sitting of Zazen ... the entire universe manifesting itself on the Zafu at that moment ...
... in other words, when the "little self" is thereby put out of a job by the experience of "just sitting" as whole and complete with nothing more to be desired or needed ... then the hard borders between the "little self" and the "not the self" (which is usually being judged and "bumped into" and divided into pieces) thus naturally soften, fully fade away ... only the wholeness of the dance remaining ...
... then "Zazen is in itself body-mind dropped off".
Human beings simply do not know how to act an action pierced as naturally complete just by the act of the action itself, how to live life that is whole just by the act of living life.