Remember the right mind.
If Ninjutsu is misused, it is the same as banditry. Ninjutsu should be used for the greater cause, not for personal gain. (Quoted from the book of Ninjutsu, Bnasen shukai)
Ninja had various techniques based on infiltration and psychology to sneak into houses and people’s minds by setting fires, confusing people by spreading rumors. It was precise because he was such a ninja that he reminded himself not to forget the “right mind.” And as a ninja, he also made a firm promise not to use his skills and abilities for personal gain .
When Ninja were active in the war period, their goals were to “survive” and “return with useful information.” This is because fighting by utilizing the information minimizes the cost to both sides of the battle, and ultimately the battle itself. This was the “ideal” way to fight, as described in Sun Tzu’s Art of War in BC.
What did Ninja do to survive while being deeply involved in a battle? The first thing to do was to “never be seen.” If the Ninja did not hide and show off their presence, opponents would surely appear, and they would have to fight each other. (in reality, even today, similar things happen everywhere, don’t they?) If they were too conspicuous, they might be shunned not only by their enemies but also by their employers. To avoid such sterile conflicts and dangers, they continued to work in the shadows. They were exceptionally mentally mature.
They only focused on accomplishing their missions and did not take pride in their achievements or leave a name behind. In this way, the Ninja supported the land and the lord of the castle in a different way from Samurai.
The Samurai, who lived in the front stage, and the Ninja, who lived in the shadows, both fulfilled their roles and functioned as a dual force, which made the times so dynamic.
The character for “忍Shinobi” has a “刃・blade” on top of the “心・heart.” It is said to represent (1) a person who constantly disciplined himself by placing a blade on his fragile heart, (2) a person who disciplined his actions by placing a blade in his own heart that would hurt others, or (3) a person with a steadfast heart who would not move even when confronted with a blade.
Ninja always faced their own minds and continued to challenge their own limits steadily and tenaciously.
I think the difference between the Ninja and the bandit was that the Ninja had the spirit to come back to the “right mind” despite their struggles.