‘In sense perception psychology, it is taught that the scope of what we can perceive is quite limited. For example, people are able to perceive sounds anywhere between a vibration frequency of 20 per second on the low end to 20,000 vibrations per second on the high end. We are not able to perceive sound outside of this range which is to say such sounds do not exist for us. That does not mean, however, that those sounds do not exist at all. There are animals that can perceive such sounds and it is also possible to detect them by means of machines. In the same way, we have a horizon (a line that marks the limit beyond which perception does not reach) that limits our perceptions and so it is only natural that it isn’t possible to grasp completely the whole of infinite zazen. No matter how we try to perceive it, the zazen we glimpse is only one part or one side of it.
Within his writings, Dogen Zenji discussed various aspects of the limitations of perception. For example, in Fukanzazengi, there is the expression “a glimpse of wisdom.” “To glimpse” means that no matter how hard we try to perceive the whole of zazen, we will never be able to see more than one part of it. This is to say that with these words Dogen Zenji cautions us to be careful of feeling some kind of ecstasy as a result of getting into some position where we cannot move because we are caught by that experience. No matter how profound and refined the insight, or delicate and subtle the perception might be (that in itself is a valuable thing…), it is limited as it is a human perception and inevitably is partial or one-sided.’ (from the Soto Zen Journal)