Favoritism is a sad but common part of many family dynamics. Being the child who their parents didn't favor can lead to a lifetime of striving to please people and feeling like they'll never be good enough. There's enough competition at school and work that there's no need for it in families. Competing for the basic feeling of being loved can have highly negative effects on the competitors, and yet some parents facilitate it. There are so many reasons a parent could favor one kid over another, and almost none of them are anything the child can control. Sometimes, parents wanted a different gender for their baby, or they didn't want the number of kids they ultimately had. Maybe they're judgemental about a child's appearance or achievements outside of the family and prop up the child they see as superior in those categories. The 15-year-old girl in this story has been through the ringer regarding favoritism, and it's heartbreaking to read about.
This image is for illustration only, and the subjects are models; the image does not depict the actual subjects of the story.