One of Alfred Adler's significant contributions to personality psychology is the theory that a person's birth order influences their personality. He hypothesized that older siblings tend to become overachievers to compensate for having to share parental attention after a new child is born. In contrast, Adler suggested that the youngest children might become spoiled. He proposed that the middle child has the opportunity to offset the negative dynamics of the oldest and youngest siblings. It is important to note that despite its popularity, research has not provided conclusive support for Adler's hypotheses on birth order.