From Deshimaru Roshi’s Q+A:
Master Dogen had gone to China to find true wisdom, to understand Zen. He studied many things but he did not really understand. In those days the religion of Buddhism, of Zen, was very widespread in China and he went from one temple to another. Nevertheless, he was not satisfied with the teaching he received so he decided to go home to Japan. Then one day he came to another temple. It was summer, and very hot. There was a very old monk there working, drying mushrooms. Old and frail as he was, he was spreading the mushrooms out in the sun.
Master Dogen saw him and asked him, “Why are you working? You are an old monk and a superior of the temple. You should get younger people to do this work. It is not necessary for you to work. Besides, it is extremely hot today. Do that another day.”
Master Dogen was young then. The old monk’s answer was most interesting and has become famous in the history of Soto Zen. It was a satori for Master Dogen. The monk said to him, “You have come from Japan, young man, you are intelligent and you understand Buddhism, but you do not understand the essence of Zen. If I do not do this, if I do not work here and now, who could understand? I am not you, I am not others. Others are not me. So others cannot have the experience. If I don’t work, if I do not have this experience here and now, I cannot understand. If a young monk helped me to do the work, if I were to stand by and watch him, then I could not have the experience of drying these mushrooms.
If I said, “Do this, do that. Put them here or there,” I could not have the experience. I could not understand the act that is here and now. “I am not others and others are not me.” Master Dogen was startled, and he suddenly understood. True, he was highly intelligent. He said to himself, “I had better spend a little more time here in China.” He had studied in books, he had looked with his brain and he spent all his time thinking, but just then he understood: “If I do not have the experience I cannot understand true Zen. Zen cannot be apprehended by the brain.” The old monk and Dogen communicated to each other. Master Dogen was startled and deeply affected. However, he went on: “Why are you drying those mushrooms today? Do it some other day.” To which the old monk answered, “Here and now is very important. These mushrooms can’t be dried another day. If this moment is lost it will not be possible to dry them: perhaps it will rain, perhaps there won’t be enough sun. You need a hot day to dry mushrooms, so today is the right time to do it. Now go away, I have to work! If you want to find true Zen, go see my master in the dojo.
“So Master Dogen went to see the old monk’s master and learn from him. At last he understood true Zen, which he had never been able to understand before. Master Dogen spent a year in this temple, then received the kesa of transmission. Afterward, he went back to Japan. But the founding principle of his philosophy always remained, “Here and now, other people are not me, I am not other people. If I do not practice I cannot understand. If somebody else does something, I cannot be in what he does.” That’s the first point. The second is “shikantaza only zazen.”
Koans are not necessary, thinking is not necessary: only zazen. Descartes said, “I think, therefore I am.” I say, “I do not think, that is why I exist.” If you create your own categories, if you think too much, you limit your consciousness. But consciousness is as deep as the cosmos. It is connected to the cosmos. If you don’t think, your consciousness becomes eternal, cosmic. That is extremely important. If you think during zazen you cannot reach the cosmic consciousness because you limit yourself. You cannot reach the limitless. When you don’t think rationally, you can think unconsciously. If I do not think, I exist here; I do not think, therefore I am.