Parents are children's first teachers, or the best teachers. Parents' innate words and deeds affect a child's life, including his character and principles.

Then there is school education:

School education also has a great influence on a person's character. The quality, content and quality of a school education system directly affect the growth of students.

Then there is the influence of classmates:

Everyone has his own small circle, his own friends, and who he often gets along with, which will also affect a person's character, because their words and deeds have a great influence on others, especially nowadays people like to follow the trend, imitate and follow others. ...

Finally, the influence of society:

Local social atmosphere, local customs and habits will also have an impact on people's character, including many things seen and heard from the media, all of which have their own understanding. Whether the local law enforcement is strict or not and whether the folk customs are simple or not will have an impact on a person (here it should be changed to a group of people). ...

The formation of a person's personality goes through many complicated processes, which can't be summarized in a simple sentence, so I will say so much first. ...