siblings, spouses, significant others &/or w/relatives, why do so many OLDEST children seem miserable, malcontented, highly critical, disdainful of others, & generally dissatisfied? What causes so many oldest children to not get along w/others? Many oldest children are always complaining/griping about their situation. They bemoan at how unfair life has been & still is to them. They talk about how without them, nothing would function. They even assert that others are totally clueless in comparison to them.