Birth Order

This one is actually more complex than it seems. The idea that children exhibit behaviour that corresponds to the order of their birth relative to their siblings is a very old one, but some have also suggested that the way a child perceives themselves in the hierarchy of siblings is just as important. Essentially, if you have an older sibling who acts like a younger sibling, and you act like an older sibling, you might have the reverse personalities of what is typical. Older siblings tend to like rules and order, and younger siblings to be carefree.