One of the best examples of a character being molded by his environment is Bernard, Charley's son. This is especially apparent when contrasted to how the environment molded Biff.
Charley, who is Willy's neighbor, had consistently been Willy's (perhaps only) friend throughout time. He was also Willy's neighbor. He is aware of Willy's problems, and accepts Willy's requests to have money "loaned" him, money that will never get paid back.
It is Charley's son, Bernard, who represents the man that is his father, Charley, thus showing that healthy, humble, and solid parenting far surpasses the paradigms that Willy Loman lived by.
Willy raised his children in complete contrast to how Charley raised his. Willy, who referred to his children as "Adonises", strongly believed that physical attractiveness, athletic prowess, and popularity are the key elements to be successful.
Willy saw himself reflected in his children, Biff and Happy. Biff, who was a popular high school football hero, was allowed to be cocky, disrespectful to teachers, and even got condoned for stealing balls from his locker room. Willy went as far as to blame Biff's teachers for not "giving" Biff the passing grade that he needed to graduate high school.
All of these dynamics created two kinds of monsters: One is Happy, the oblivious and immature younger son who grows up to be a liar and irresponsible adult. The other monster is Biff, the once super star, who is now a nearly-broken man that cannot anchor anywhere, has not grown up emotionally, and has remained stunted in time living a fantasy life.
As a child, Bernard was regarded by the Lomans as the least-liked and unpopular "nerd" that followed the popular Biff around. Willy would laugh at Bernard because of his smaller size and demure attitude. He also would laugh at Bernard's father, Charley, stating that the latter would have wished to have a kid like Biff (in not so many words).
However, Charley never antagonized Willy, with the exception of a time when he and Willy got into it after Charley questioned Willy's fixation with Biff's upcoming game at Ebbets field.
Regardless, the implication here is that Charley continued raising his son without false pride, nor trying to change him.
Years later, Bernard, now an adult, is sitting in his father's office's waiting room when Jenny, Charley's secretary, comes to get him and asks him to please deal with Willy Loman. Willy was having that Ebbets Field flashback.
Willy learns that Bernard has become a lawyer. A defense attorney on his way to defend a case in the Supreme Court. Here is the key difference between raising a shallow child and an honest one. Even Willy was in shock:
BERNARD: What is it Willy?
WILLY [small and alone]: What-what’s the secret?
BERNARD: What secret?
WILLY: How—how did you? Why didn’t he [BIFF] ever catch on?
BERNARD: I wouldn’t know that, Willy.
WILLY [confidentially, desperately]: You were his friend, his boyhood friend. There’s something I don’t understand about it. His life ended after that Ebbets Field game. From the age of seventeen nothing good ever happened to him. (Act 2)
To add to the wound, Willy knows that part of the problem was Biff's discovery that Willy was having an affair with a woman from work; something that tore him from the inside, since Willy had built himself as a model for Biff to follow. With no heroes, Biff realized how much his life was intertwined with Willy's. This is the great contrast that exists between he and Bernard. Bernard was able to become his own man, his own person. This is why he ended up succeeding and Biff became a hanger on of his parents. The environment molded both young men growing up. The results varied entirely from one person to the other.
Characters can be influenced by their environment in different ways. Willy Loman for example is challenged by his physical environment. As an aging traveling salesman his depression is enhanced by his extended travel. This ultimately causes him to ask for a more profitable and easier route in New York, his home. This request is not only denied, but he is fired from his job which leads to his demise.
Willy is also influenced by his perceived environment. His delusions create confusion for him because he remembers and lives events at the same time. These delusions create a confusing environment for Willy and cause him to become angry at many points in the story with his son Biff and neighbor Charley. Part of his environment is his own fault because his wife supports him, but he lies about his finances due to embarrassment.
Willy is influenced by his physical limitations in terms of sales, and also mental limitations.