Shinobi Rules

Upon becoming a shinobi, one must abide by specific rules when out in the field. Ninjas follow this code in order to "kill their emotions", preventing them from running wild and causing the mission to fail. The most important thing for a shinobi is to be a tool for achieving their village and country's goals. Emotions are unnecessary things. These rules are often taught at Ninja Academy.

Konohagakure Rules

 * 4. "A shinobi must always put the mission first."
 * 25. "A shinobi must never show tears."
 * "A shinobi must see underneath the underneath."
 * "A shinobi is to never question their leading ninja."
 * "A shinobi will prepare before it is too late."

Kirigakure Rules

 * "A shinobi must never show attachment."

Breaking the Rules
A running theme in the series is that a shinobi is still human, and that ninjas may not be able to completely be emotionless tools. Minato explained to his students that while the rules and regulations are important, they are not infallible. A ninja must also know when to break these rules in order to adapt and cope with the situation. For Kakashi, his belief is that "while those who break the rules of the ninja world are considered trash...those who don't take care of their comrades are even lower than trash." In Naruto's case, he doesn't believe strictly following these rules will make him a true ninja, and has decided to be a ninja in his own way.