At first I thought having a little sister was going to be horrendous. Little did I know she'd grow up to be my best friend.
Having a little sister makes you want to be the best version of yourself. You want to show her how she should act and be treated. It's like you're the example. You want to be the best you can be so she is proud.
Having a little sister makes you overly protective. If anyone even looks at her the wrong way you probably already want to attack. She makes you realize how precious life is, how much one person can mean to someone.
Having a little sister makes you realize how angry you can get. She will push and test your limits but that is okay-- that's what she's for. She makes you realize what bothers you the most.
Having a little sister gives you a lifelong friend. Someone you confide in. Someone you share stuff with (most times). Someone you can always hang out with. Someone who will always pig out with. Someone who you love forever.