Research suggests that first-borns tend to be highly ambitious and competitive and excel academically.
According to a 2013 study, it's thanks to their parents, who give them their best parenting but ease up on kids born later. As Derek Thompson points out at The Atlantic, international surveys of birth orders and behavior suggest that first borns tend to have higher IQs and perform better in school across the globe. "Looking at parent evaluations of children from the National Longitudinal Survey of Youth in 1979, the researchers found that mothers are much more likely to see their first children as high-achievers. They regard their subsequent children as considerably more average in their class."
By contrast, the youngest siblings are often the most creative and entertaining in their families, which in some kids can help them end up in creative roles or mid-level management.
Finally, studies suggest that only children tend to be more self-centered and success-seeking, and can also be unusually mature because they spend so much one-on-one time with their parents. Like first-borns, they can end up in C-level or six-figure positions, but tend to be less satisfied with their jobs than people with siblings.
Source : http://www.businessinsider.com/surprising-things-that-affect-success-2017-1228