The primary environmental factor which affects the young David Pelzer is the abuse he receives from his mother. She puts him through numerous forms of physical abuse, such as starvation, the inhalation of chemicals as a form of punishment, being stabbed, and being forced to swallow ammonia. David undergoes emotional abuse at her hands, including his mother threatening to burn him alive, her forcing his siblings to never call him by his name and only by using "the boy" or "it," and his mother's deceptively kind behavior just before social services comes to investigate. He also experiences verbal abuse, like his mother calling him a "little shit" and telling David that he's an embarrassment to the family.
In a wide variety of ways, David's sense of emotional stability is eroded by the woman who is supposed to be his best source of encouragement and safety. He tries over and over to please her, but he continues to suffer increasingly dangerous forms of abuse until a teacher finally reports the situation and he is removed from his mother's care.
The biological factor that most shapes this situation is David's young age. The abuse begins when David is around 6 and continues until he is sent to foster care around age 12. He is so young when the abuse begins that his primary concern is making his mother happy; his sense of the world is not yet capable of realizing that he has no control over his mother's mental instability. When the abuse first begins, his mother often sends David on searches for her imaginary "missing" belongings that can never be found. During these episodes, we hear David's young voice of desperation:
I imagined myself marching upstairs with my prize and Mom greeting me with hugs and kisses. My fantasy included the family living happily ever after. But, I never found any of Mother’s lost things, and she never let me forget that I was an incompetent loser.
Young David doesn't yet realize that having a healthy mother is a "fantasy," so he desperately continues trying to find a way to make her happy. His mother takes advantage of his young and impressionable mind, always reminding David that he is a "loser." She uses David's fears and his need for her love to manipulate her son.