Why are firstborns bossy?
Firstborn children are thrust into a leadership role from the time they gain a younger sibling. That spells decades of at-home leadership experience, which, at times, could be plain bossiness. They like to be in charge. A few firstborns will have trouble delegating; they will not trust others to do the job well enough.
What is older sister syndrome?
When the elder sibling grows up, he (or she) becomes totally ashamed of what he (or she) had done. Usually, the siblings as adults will never even discuss what happened. They may go on and act like nothing at all had ever happened. They may avoid one another, but sometimes they may even become quite close!