There are two unique characteristics of Antaiji sesshins. One is that there is absolutely no talking. There are no greetings or socializing, and not even any of the sutra-chanting that might happen at other times in a temple. Usually the head of a Soto Zen temple does not face the wall but rather faces the rest of the monks or practitioners to watch over them, but I always face the wall along with everyone else. These are the main characteristics of Antaiji sesshin. The only instruction added to these rules is that you apply yourself to your own practice regardless of anyone else. I began this style of sesshin after experiencing various types of sesshins and I have continued this practice since 1965 because I believe it to be the purest way of putting into practice the words of Sawaki Roshi: "Zazen is the self doing itself by itself."
When we sit facing the wall day after day in sesshin without the usual entertainments of temple life -- dokusan, meal chants, work period, dharma talks, liturgy, etc -- the sesshin becomes one long period of shikantaza. Because we stay inside the sesshin container, we never forget that we're there to let go of thought. Without various kinds of external stimulation, it's difficult to keep up our usual intellectualizing for five days straight. Although we might feel sleepy, Uchiyama Roshi says we don't need to worry because no one sleeps through an entire sesshin. We let go of thought or wake up on our own and return to the self that is only the self.
When practitioners first decide to participate in sesshin at Sanshin, sometimes they feel a bit intimidated. On one hand, the simplicity of the days is appealing. One doesn't need to know how to do liturgy or have something impressive to ask or say during dokusan. Other than a few basic zendo forms, the only thing one needs to know how to do is sit. On the other hand, all those long periods of shikantaza, hour after hour and day after day, can be physically and psychologically demanding. Back or knee pain, boredom and fatigue are not uncommon. Surely one has to be young and athletic and have had a few peak experiences in order to sit this kind of sesshin!
But simply powering through the days, gritting one's teeth, enduring the pain and unwelcome thoughts, is not the point of sesshin. Liberation comes when one stops struggling against the sesshin and gives up ideas about comparing one's stamina with that of the others in the zendo or in one's home sangha. Sesshin is not about forcing ourselves to sit a punishing schedule in order to prove our worth. Neither is it about pain for gain, expecting a spiritual reward for our virtuoso display of shikantaza. We give up all that stuff during sesshin and settle into just being our truest selves in each moment rather than time-travelling to the end of sesshin in our minds, when things will be better somehow.
During the sesshin, 50 minutes of shikantaza alternates with ten minutes of kinhin. When kinhin is the only thing we have to play with, it can be a bright spot of distraction that comes around once an hour. Certainly, it's fine to take those ten minutes to leave the zendo to use the bathroom, get a sweater, or take care of other necessary business. However, about halfway through the sesshin, somehow every time the kinhin bell rings nearly everyone leaves the zendo. Suddenly it's become extremely important to get a drink of water, check on one's belongings or look at the weather. An hour later, it's something else. Everyone has come up with a reason to get out of the zendo, look at something different and "take a break" from shikantaza.
The problem is that there is no escape from shikantaza mind. We keep that same shikantaza mind of letting go of thought throughout all of the activities of the sesshin day. Our practice is not about what we're going to do when we get into the zendo or out of the zendo but what we're doing now -- and it's always now. It doesn't matter whether you're sitting or doing kinhin, using the toilet, doing kitchen cleanup, or going to bed -- it's all the same mind, so there is no break or escape from shikantaza.
During sesshin, others are helping you by making and serving your meals, watching the clock and ringing the bells, and making and posting work assignments. You don't need to make those decisions, so you have the rare opportunity let go of discursive thinking. To look for a break or some variety or distraction during this style of sesshin is to work against the very container into which you've put yourself, a container that supports maintaining constant shikantaza mind throughout the day. When you've just spent 50 minutes letting go of thought, it doesn't make sense to spend the next ten going outside in search of something more interesting. If you find yourself casting about for a reason to skip kinhin, it's better to stay in the zendo.
The same goes for the unscheduled time after meals. That's not the time to peruse our library and engage in dharma study, for the same reasons that our sesshin is conducted without any talking or chanting. During shikantaza, we let go of all thinking, including thinking about the dharma. Filling your head with reading, chatter or devices during breaktime is counterproductive for yourself and others.
As Okumura Roshi frequently says just before the opening zazen period of a sesshin, don't distract others and don't be distracted by others.