Sibling Rivalry is the common answer on why you don't get along with your brother or sister and then eventually we grow from it.
As for mine own, it is true with my sister who is the baby of the family and grandmas's favorite. She knew her tool and how to manipulate to get what she needs. Due to her supreme intelligence and having me do her dirty work she was the baby. My sister and I shared a room so we had fights about the television, clothes and borrowing my car. She never asked me and always told my parents that she did ask me. We got to the point where physical violence began. She made her goal to move out by she was 21 and did 3 months prior to her birthday.
Today she is a successful manager of a Home Depot store with no debt and in the process of looking to purchase at her own home. I will not lie but yes I am feeling the rivalry, but more in the fact why did I not have the determination and individualism she carries.
I also have two brothers which unfortunately I do not speak to or have spoken to in the past 16 years. I have seen them in passing but they have been cut off from the family. Other than bad things one of my brothers did that I prefer not to speak of.