Not Setting The Mind
From Trevor Leggett’s “Zen and the Ways” Shambhala page 138

.. In Tokugawa times, one of the big Jujutsu schools lost three of its best men, killed at night in the street. In each case there was only one mark on the body, a stab in the abdomen, slightly to the right side. It was guessed that these killings were done by a member of a rival school, with which there was a feud on, but the puzzle was how these three highly skilled men could have been killed by one clean stab. If they had been overcome by numbers there would have been other marks; a single man, even though armed, could hardly have finished the fight with one blow, especially a thrust to the abdomen which is easily checked.

The experts finally worked out how it had been done,. There are only two effective ways of using the stabbing knife, (1) from below to the abdomen, and (2) from above on to the neck and shoulder. Skilled Jujutsu men were well practiced in the defense to both of these attacks. An expert could tell which attack was coming by observing the position of the attacker’s right hand: if the thumb is in front, the attack will come down, and if it is to the rear, the attack will come upward. Before the blade is actually visible, the defender’s body is already moving into the defensive reaction.

The other Jujutsu school had discovered how to make use of this fact. Their man was holding the knife reversed; his left hand holding the hilt, and the right hand holding only the sheath. This right hand had the thumb prominently displayed – in front. So the defender was moving to intercept a downward blow, but when that came it was being made with the sheath, while the blade moved upwards unopposed.

This is an example of getting the mind set on one thing, namely the position of the opponent’s thumb, which in the ordinary way is the key to the entire situation. Does this mean then that the thumb is not to be noticed? No, It is to be noticed, but not at the expense of the whole situation. As a matter of fact, the opponent’s posture is not the normal one which of a man about to draw a knife with his right hand. The opponent is holding the knife in fact in his left hand, and he will have to advance his left foot to use it. If we look at the posture … we see that from the very beginning the knife-man has his left foot level with his right foot, whereas in the normal it is well back. An experienced Judo expert, who does not let his mind become set on the thumb position, will find something ‘unusual’ in the situation. He will not be tied to a mechanical defense reaction.