Inés Brock-Harder, chairwoman of the Federal Association for Child and Adolescent Psychotherapy and therapist for sibling problems, says siblings are an underestimated resource. Brothers and sisters don't always stick together through thick and thin.

There are indifferent or negative feelings towards siblings, just like brother and sister. Up to six arguments per hour are normal, according to experts. The sibling relationship shapes our lives, for better or worse, says Inés Brock Harder, a therapist for children and adolescents in Germany. The relationship with them is the longest that we have in our lives. “And we know today that they shape us more than our parents,” she says. The age difference plays a special role. Children one or more siblings showed increased depressive symptoms or distance between them. The greater the distance between the siblings, the better they were off. The only advantage children share with siblings is that they share resources with them over them, while the resources that siblings can give each other are not reflected in them.