The strings of the lute of Zazen should be neither too tight and binding, nor too loose and lax. Then, picking up the instrument, simply play the music forgetting before and after. Each single note or notes expresses the entire song, and fully contains the symphony of all reality. Musician, instrument, strings, note and the entire symphony are one. Such is the music of Shikantaza.
Of course, the fellow playing for ten years will be better than the person on the first day. One hopes for harmonious notes, and not to be off key. However, as strange as it sounds, the person on the first day who makes a mess of it, and the maestro on the concert stage are playing the very same Symphony which expresses to the Buddha Ear a Harmony that fully embodies both the 'off key' disharmonies and ordinary harmonies that a small human ear thinks it hears. This is the Harmony of Shikantaza.
Thus, there is nothing to achieve, and no mistakes or playing badly. The careless hack and the experienced master are one and the same, each and all Buddha playing Buddha. However, there is playing badly, and the hack may not realize such fact of the Harmony which sweeps in harmony and disharmony, so we practice diligently each day. The beginner need not Practice to become a Master, and no Master can be made, but only a Master truly realizes this fact. That is why Practice does not matter in the least, so we Practice each day not too little of too much:
One may break a string or all may go smoothly, every note right on time. However, in this Symphony, there is a Big S String that vibrates but which never can be broken, and no Time to be on or ahead or behind. There is no right duration for Practice, Practice never starts and never ends ... thus we Practice each day with beginning and end. The show never starts or finishes, so we begin to play at 7:00 for however many minutes that are required.
To truly know this achievement of the Harmony that holds all harmony and disharmony, one practice forgetting before and after, all achievement, beginners of a day or masters of many years. Please continue to do so note by note for many years.
I hope the image helped people better understand. One of my crazy metaphors for Sitting beyond time, achievement, wrong notes or right. One does not hear this music with ordinary ears. One does not "practice" in the usual way with an eye on the calendar or clock.
The metronome of Sitting strikes once, for several minutes or days, for countless eons, back to front which is front to back, future to past, and never is turned on at all. One is all and all just one.

Gassho, J