A new mother is pulled between two identities that each demand all of her, so doing well at one means doing badly at the other. Unlike other conflicts of love, this one cannot be settled. She is not herself with her children, and not herself without them.
Motherhood runs on expected conformity, and breaking free of it takes some kind of violence. So a mother who says openly that it is not pure joy is treated as breaking a taboo. Her honesty can bring public outrage and even claims that she is unfit to raise her children.
Full-time care for a baby wears down a woman's self-esteem and her place in the adult world. Her social self gives way to the job of keeping another person alive. Motherhood works like a fenced-off compound where the group's claims outrank the individual, and she keeps planning her escape.
Looking after a baby is the hardest work there is, yet it produces nothing anyone can point to. It is like being in charge of the weather or the grass growing. The days have no landmarks, and what the job finally asks for is simply being there, enough and present.
Almost nothing of what mothering is really like survives being described to the outside world. That makes the work invisible. It also leaves mothers alone with it, so an honest account can work as company for others in the same place.