Happy Loman represents the child that had the bad fortune of being less athletic than his brother. As a result, his father's affection was focused only on his older brother Biff, and he was regulated to the background. As a result, his whole life has been an attempt to gain attention. From the recurring assertion "I've lost weight!" to his philandering ways, Happy continually seeks validation and the interest from other people.
Unfortunately, he has also adopted some of his family member's bad judgment. Like his father, he tends to exaggerate his and his family's worth, and like his brother, he will lie to avoid troubling conversations or situations. Like his mother, he tends to enable the traits of his father and brother, rather than seek to help them.
Happy's childhood crippled his ability to honestly seek and hold relationships and to tell the truth about himself and his family members.