Three crucial aspects of the environment are parents, peers, and particular situ

Parents have little direct influence on personality; however, the child’s personality is shaped in part by the two-way interaction between parent and child.
Peers often have a very strong impact on personality development.
Though people have a set of central or core traits that are relatively stable, their behavior can vary across situations.
There is a continual two-way interaction between an individual (including temperament, learned habits, perceptions, and beliefs) and aspects of the situation (such as opportunities for reward or punishment, chance events, etc.). 
This interaction is called reciprocal determinism.
In sum, core personality traits may stem from genetic dispositions, but they are profoundly shaped by learning, peers, situations, experience, and the culture.