This is the story told to me.
A 38 year old woman, Anne, married with three kids, has a 17 year old brother, Tim, who still lives at home with his (and Anne's) parents. Tim got his teenaged girlfriend pregnant. Oops. Should he have an abortion?
While he felt he could tell this to his big sister, he definitely did not want to tell his parents. They were crazy-- a fact corroborated by Anne. They weren't just strict, they were almost delusional. Denial, avoidance, displacement were the main coping styles; do nothing was core policy. Bill too big? Procrastinate. Coughing up blood? Humidifier. There was plenty of affect there, especially anger, but it was always focused on arguing about the problem, never solving the problem. "All those stupid doctors will do is charge my insurance thousands of dollars and then say they don't know anything. Crooks, crooks I tell you!"
Of course, Anne and her husband were highly conflicted as well. Wrestling with the reality of an abortion, or not, and that they had been sworn to secrecy. They couldn't tell the parents. Everyone was in full agreement that the irrationality of the parents would make any decision at all nearly impossible. The teens would eventually have the child not because they chose to, but because of paralysis.
Not a spoiler: Anne has to get on the phone right now and call her brother and say the following words: "if you don't tell mom and dad in the next hour, I will." And hang up.
Anne's job is not to protect Tim from their insane father. If Anne wants to be supportive, she can say, "I'll come with you to tell them, and I'll help calm the Unabomber down."
By not telling, Anne sets herself up to be hated by both the parents and her brother. The parents will, of course, say, "how could you not tell us? He's our son, he's a minor! How would you feel if this was your kid!?"
In ten years, her brother will get to say, "you know, that was the hardest decision I ever made, and I wasn't really mature enough to make it, and by not telling, you let me make it alone. Basically, if it hadn't been for you, I would never have gotten an abortion."
Tim understandably didn't want to tell his parents. But instead of owning his decision and not telling anyone, he brought his sister and husband into it. Why?
The therapy answer is, "he wanted some support." But really, he wanted to unload a heavy secret, discharge the energy. He wanted to get to the "I feel better just talking about it" stage. The shame part had been overcome. Now he was free to decide what he wanted to do.
This is why he chose to tell his adult sister. It wasn't because he valued her advice and wisdom. He told her because she was an adult, a parent of three kids. That's the next best thing to telling your own parents. And so if Anne was ok with not telling her parents, then for sure he could be okay with it. Adult decisions, made by an adult.
Of course, by unloading, he had loaded her up. He didn't care about that. Instead of him being up all night thinking, "oh God, what have I done?" he was sleeping. Free of morality and ethics and shame and guilt, he could focus on logistics. She was the one up all night, "oh God, how did this happen? What should he do? What should I do?"
In short, Tim had chosen the worst possible posture: passive-aggressive. He didn't take his burden on his own shoulders, like a man, and not drag anyone down with him; nor did he assert himself, again like a man, and tell everyone what had happened and what he had decided, and take the consequences. No. He boldly asserted his autonomy on someone with no power over him and hid from the people who had a lot.