From Chapter 3 ("Nothing Extraneous") of Subtle Sound: The Zen Teachings of Maurine Stuart, on letting go of goals and just sitting:
When we practice zazen we give up everything. We give up thoughts. Of course they come, but when they do, we give them up. We give up wanting something from our zazen. We give up any idea of becoming enlightened. To become enlightened is the most important thing in our lives, but to have thoughts about it is no good. We give up all extraneous thoughts about our sitting. When they come, we give them up. And we don't move! When the body moves, the mind follows; and when the mind moves, the body follows. We harm our practice when we move. We have to start all over again. So we take the time to set up our posture, and then we sit absolutely still.
... and the closing words of that chapter:
... We drop off all extraneous matters and just do zazen; just let zazen do us, with absolutely meticulous attention. Attention! Attention! Attention! Nothing more, nothing less.