Andrew Seddon

“You must realize that no matter how intently you count your breaths you will still perceive what is in your line of vision, since your eyes are open, and you will hear the normal sounds about you, as your ears are not plugged. And since your brain likewise is not asleep, various thought forms will dart about your mind. Now, they will not hamper or diminish the effectiveness of zazen unless, evaluating them as "good", you cling to them or, deciding they are "bad", you try to check or eliminate them.”
― Philip Kapleau Roshi, The Three Pillars of Zen: Teaching, Practice, and Enlightenment