A parent who despises himself deep down. This parent can appear to be quite loving of her children, so she can be difficult to spot. But she is unable to tolerate certain aspects of herself, so she projects those traits onto a chosen child, and despises him instead. It is an unconscious coping mechanism that happens outside of the parent’s awareness.

The best and the brightest. This child threatens to outperform or outshine one or both of the parents. Either consciously or unconsciously, the parents sabotage her to hold her back. This way, they won’t lose her and they won’t have to feel badly about themselves in comparison to her.

Sibling rivalry. In this family, there is simply not enough attention or love to go around. One or both of the parents is limited in some way; by mental illness, personality disorder, or substance abuse for example. The siblings must jockey for whatever they can get.

Childhood Emotional Neglect (CEN): the child who is the most invisible. In this family, all of the children may get the subtle (or not-so-subtle) message that their feelings don’t matter. But one is better at hiding his own needs, feelings, and self than the others. This child literally disappears from the family’s radar screen and is ignored. He becomes persona non grata. He is the one who matters the least.

The child most prone to depression or anxiety. The child with intense or dark feelings or thoughts which the parents cannot understand may frighten them. At a loss about how to help, they may just keep him at a distance.

The child who has the least in common with the parents. This child sticks out because of his personality, temperament or interests. The parents are baffled by him and inadvertently treat him differently, which spreads to the siblings. source