In my view, the following are some common misunderstandings regarding Shikantaza. Or, better said, different baseball teachers may teach somewhat different ways to throw the ball. This is as I see it and emphasize here ...
I - "Just Sitting" is only to sit in the "Full Lotus Position" and no other position:
Japanese culture can be a bit rigid and incessant on the one "right" way to do any action, be it to pour a cup of tea (this is a cultural aspect of the traditional arts) or crossing the street, and about pushing oneself to conform to that 'One Way or the Highway' ... called a 'Kata' (if anyone has martial arts experience). Such teachers may tend to emphasize that the one and only way to sit Zazen is in the "Lotus Position". Here is a little description of "Kata" (I cannot verify the source of the following, but I can verify the conclusion from 20 years living in Japan):
On the other hand, as with Oryoki eating (a wonderful example of "Kata"), there is a beauty in the fixed form that one literally can lose ones' 'self' in. So, "Kata" is also a very very good thing, don't misunderstand me on that point. Conforming to "classic" form has very many beneficial aspects. I am a big big fan of Oryoki and other Kata practices, and I teach them. In fact, Dogen seems to have only talked about the Lotus Position (no seiza benches for him in the 13th century), and my own teacher, Nishijima says that folks should sit in the Lotus Position (and he is not too open to alternatives ... he rightly says that some folks reject the Lotus position and such before really giving it a try). Uchiyama Roshi has said some things in his book that place him more or less in that category..... an immovable set of rules that govern what is and what is not accepted as acceptable behavior or thinking in japan ... In reality, there are many “Ways” to do most things in Japan, although each group will have a tendency to claim that its pattern is “the Way.” As a medical researcher who has participated in procedures and experiments at many dozens of Japanese hospitals, universities and the like, I know that no two groups ever will follow exactly the same patterns. Each, however, will have a tendency to explain that its way is “the Way,” usually because the most senior person in the group will have come to that conclusion after having learned it to be the thinking of some other person ... that the senior person respects. (Also, one must be very careful in suggesting that a competing group might have a better way which contradicts the opinion of a senior member of group). Every group in every culture does this, but what is unusual in Japan is the inflexible, almost mechanical way the system operates. The emphasis on proper “Kata” (Boye de Menthe has a wonderful, hard to find little book on this) in Japanese society is reminiscent of any conservative, tradition based culture, though unique in the way is has developed to permit a functioning, industrial society.
But when this is carried too far, the "Lotus Position" itself can come to be thought of as having some "magic power", or fetishized as working some miraculous psycho-physiological effect on the body to lead to "Satori". But that is not the meaning, I believe, of "sitting in the Lotus Position is enlightenment itself".
It is, rather, "sitting in the Lotus Position as a 'pure' act, the one and only act in the universe at that moment'. The Lotus Position itself is not the point. It is "doing one pure act in one moment". (Although, truly, the Lotus Position does have many advantages in allowing us to forget the body, and balance the body, leading to balance in mind ... chair sitting, for example, is just not as good in that way)
Well, in the fat thighed, bad back West, many folks just cannot manage the Lotus Position. So, the emphasis has changed slightly: As opposed to "sitting in the Lotus Position as a 'pure' act, the one and only act in the universe at that moment' ... it has changed to 'sitting as a pure act, the one and only act in the universe at that moment'. In other words, "sitting in a chair is enlightenment itself' is true too if approached with that attitude. Do "chair sitting" as a Kata!
By the way, while Dogen and others emphasized that sitting Zazen is "enlightenment itself", they also taught that everything is "Zazen" if approached that way. Dogen sometimes said that Zazen is only sitting (not walking, running, standing or lying down), but he also said that Zazen is walking, running, standing or lying down (that guy knew how to talk out of both sides of his mouth!) So, I teach that perspective too here at Treeleaf.
2- The point of "Shikantaza" is "Not Thinking".
All through the history of Buddhism, and many Eastern religions, has been the emphasis by some on attaining states in which thought and perhaps all consciousness are extinguished in various ways. There are forms of meditation that do reach such states. We may even, at times, experience this in our "Shikanataza" meditation. However, I believe that Dogen's meaning of "think not thinking = non-thinking" is much more subtle than this, much more practical. Dogen wrote this in his Fukanzazengi ...
I describe "nonthnking" in another way too, for example, as having "thoughts, goals, likes and dislikes" on one channel ... while simultaneously dropping "thoughts, goals, likes and dislikes" on another channel, not two. It is not about always being in a state of deep Samadhi in which thoughts (and even consciousness) vanish. There is no evidence in Dogen's writings that he meant such states or that, if such a state were sometimes tasted (which we do taste), we should remain there. (I know some drugs you can inject in your veins that will get you "there" faster than Zazen!). Nor is this practice about being in a coma or a deep deep sleep. Rather, it is about being alive and awake!
"...Once you have adjusted your posture, take a breath and exhale fully, rock your body right and left, and settle into steady, immovable sitting. Think of not thinking. Not thinking: What kind of thinking is that? Letting thoughts go (Nonthinking). This is the essential art of zazen. "
Some teachers of Shikanataza, often coming from a Rinzai influence, believe that Dogen meant that we should use Zazen to attain deep states of "not thinking" as the ultimate goal of practice. I don't think so (pun intended), and I see no evidence that he meant that. Or that the Buddha meant that, for that matter.
3- "Shikantaza" should be a strenuous effort, sweat pouring from your brow as if your "hair were on fire."
Again, I usually hear this from some lineages heavily impacted by a hard "Rinzai' approach (usually connected to the "Harada-Yasutani" school, which includes the Diamond Sangha, "Three Pillars of Zen" Kapleau Roshi, the early Maezumi Roshi/White Plum lineage, Sanbokyodan and others.). Push push push to "Break through".
In fact, I believe that Dogen's way and meaning was much more subtle. I sometimes say that the Rinzai folks like to punch a hole through the wall separating "self" and "other" by using dynamite, while Dogen was like the air itself ... gently filling all the cracks in the bricks, both this side and the other, and even the bricks themselves until all is just as whole and clear as the air. Oh, there may be days to push ourselves hard ... times to just relax and go with the flow ... but, in all cases, just be the flowing.
6- Something like "Shikantaza" is only for advanced practitioners.
That was not Dogen's teaching. He recommended Shikantaza as a universal practice for everyone, and it is.
5- "Shikantaza" is a breathing practice.
Buddhism does have some forms of meditation that emphasize ways of breathing to bring about certain mental states. Also, in Soto Zen, we do teach counting the breaths and such as a way to settle the mind for beginners or at times when the mind may be unusually turbulent and disturbed. But I see no sign that Dogen meant counting the breath, or awareness of the breath as the heart of Shikantaza. In fact, he said quite the opposite, and just said to let the breath take its natural rhythm.
More on "just breathing" here ...