We spend our life until we're twenty deciding what parts of ourself to put into the bag, and we spend the rest of our lives trying to get them out again. Sometimes retrieving them feels impossible, as if the bag were sealed. Suppose the bag remains sealed-what happens then? A great nineteenth-century story has an idea about that. One night Robert Louis Stevenson woke up and told his wife a bit of a dream he'd just had. She urged him to write it down; he did, and it became "Dr. Jekyll and Mr. Hyde." The nice side of the personality becomes, in our idealistic culture, nicer and nicer. The Western man may be a liberal doctor, for example, always thinking about the good of others. Morally and ethically he is wonderful. But the substance in the bag takes on a personality of its own; it can't be ignored. The story says that the substance locked in the bag appears one day somewhere else in the city. The substance in the bag feels angry, and when you see it it is shaped like an ape, and moves like an ape. The story says then that when we put a part of ourselves in the bag it regresses. It de-evolves toward barbarism. Suppose a young man seals a bag at twenty and then waits fifteen or twenty years before he opens it again. What will he find? Sadly, the sexuality, the wildness, the impulsiveness, the anger, the freedom he put in have all regressed; they are not only primitive in mood, they are hostile to the person who opens the bag. The man who opens his bag at forty-five or the woman who opens her bag rightly feels fear. She glances up and sees the shadow of an ape passing along the alley wall; anyone seeing that would be frightened. I think we could say that most males in our culture put their feminine side or interior woman into the bag. When they begin, perhaps around thirty-five or forty, trying to get in touch with their feminine side again, she may be by then truly hostile to them. The same man may experience in the meantime much hostility from women in the outer world. The rule seems to be: the outside has to be like the inside. That's the way it is on this globe. If a woman, wanting to be approved for her femininity, has put her masculine side or her internal male into the bag, she may find that twenty years later he will be hostile to her. Moreover he may be unfeeling and brutal in his criticism. She's in a spot. Finding a hostile man to live with would give her someone to blame, and take away the pressure, but that wouldn't help the problem of the closed bag. In the meantime, she is liable to sense a double rejection, from the male inside and the male outside. There's a lot of grief in this whole thing. Every part of our personality that we do not love will become hostile to us.
— Robert Bly
Bly is describing a law, not a metaphor. What gets locked away does not wait patiently in storage — it metabolizes in the dark, and what emerges after years of confinement is not the original thing but something that has grown alien to the one who sealed it. The sexuality that was too dangerous, the anger that seemed too ugly, the wildness that didn't fit the image of the good liberal doctor — these do not remain at the developmental level at which they were rejected. They regress. They pick up a grievance. By the time the forty-five-year-old finally reaches for them, he is not retrieving himself; he is meeting something that has been waiting, and not warmly.
This is where the idealism cuts deepest. The "nicer and nicer" personality Bly sketches is not weakness — it is a genuine achievement, a real ethical formation — and that is precisely what makes the shadow so violent by the time it surfaces. The more coherent the persona, the longer the seal holds, the more feral the contents become. The outer hostility that follows — the women who become enemies, the inner critic who turns brutal — is not coincidence or bad luck. It is, as Bly says flatly, the rule: the outside mirrors what has been done to the inside. That formulation deserves to sit with you for a while before any rush toward the remedy.
Robert Bly·A Little Book on the Human Shadow·1988