Naruto characters love working in teams, especially in teams of three. One of the first things that the show teaches you is also the importance of teams and friends; how important it is to look out for each other. This pattern is not just exclusive to Konoha, but to other villages as well. During the Chunin exams, people from lots of other villages are seen in groups of three, working together to succeed.
Kishimoto emphasizes the importance of teams from the beginning of the show. The first test that Naruto, Sasuke, and Sakura went through as a team was the bell test, where they were taught the importance of working as a team. A lot of events that transpire in Naruto are among team members and their belief in each other.
Solo missions are incredibly rare in Naruto. Only a few Ninja do so, like Minato Namikaze during war. It is almost always a trio, and if one member is unable to perform in the team, it is replaced with another member from a different team.
Throughout Ninja history, teams of three had been found the perfect amount. It helps the team members look out for each other from all sides, complement each others’ strengths and look out for their weaknesses. A perfect example is the Ino-Shika-Cho team, which seem to have barely any rift between each other as they work perfectly in sync due to experience.
Teams are extremely important in the Ninja world, and Kishimoto emphasizes the importance of looking out for your friends while doing a mission, even prioritizing their safety over the mission’s success.