From Someya Sensei's book "Introduction to Shurikenjutsu" (手裏剣術入門) page 71:
In this way, the target is something that is facing the person throwing shuriken. It looks like the target is outside the shurikenjutsu practitioner. However, the true target is not facing outside the practitioner, but is the practitioner themself.
When the practitioner has dishonesty, wickedness, a bad spirit, is evil, etc, they strike outside of themselves without success. Actually, the practitioner should strike the dishonesty, wickedness, bad spirit, evil, etc, hidden inside their own body.
Now when the practitioner becomes honest and pure, they try to strike but there is no target. This is called "shin da".
Don't cast a shadow.
This is the height of Shinkage.
(Original text attached which was cleaned up from a photo of the book. Like any translation there are multiple words or ways of saying some parts that could've been used. So following on from the last post a couple of weeks ago, we see the theme common in traditional martial art training of self improvement.)
From Otsuka Sensei's book in English "Meifu Shinkage Ryu Fundo Kusarijutsu Shurikenjutsu" (red and green cover) page 143:
Do not have it in your mind that you will shoot the target.
If you do, then you are searching for more targets that you can shoot at. The thought that is seeking a target is the same thought that is seeking an enemy. To seek an enemy is foolish. Foolishness is the dark side of your spirit.
When you live a sincere life, then your spirit will have no shadows. When your spirit and deeds are pure, then you will never encounter an enemy. Then you will overcome time and space and defeat all enemies.
That is the "shin da"... the true shot.
From Danny Fletcher's book "Japanese Throwing Weapons" (another very good book) from the forward written by Otsuka Sensei:
You must not become attached to the idea of piercing the target. If you do, you may desire more targets to pierce. The heart that desires a target is the same as the heart that desires an enemy.
Desiring an enemy is foolishness. Foolishness is the darkness of your heart.
If you live sincerely, your heart will hold no shadows. If your heart and deeds are pure, then you will never encounter any enemy.
This is "Shin-da." (Truly pierced.)
(After this is a reference to a later page with the original Japanese text of this creed, which itself is a subset and overlaps the Japanese from Someya Sensei's book in the main post.)